00 Device guide v1.1.10 Release
2026-10-15
Everything your CYGM can do
Start at the top. The first section takes you from a blank screen to a live glucose reading in about ten minutes. After that every screen on the device gets explained one at a time, with a picture of what you will actually be looking at.
On this page
01 Quick start
Quick start
Five steps from a box on the table to a glucose number on the screen.
You need the device, a USB-C cable, a 2.4 GHz WiFi network, and the login for whichever CGM service you already use.
On a brand-new device you do not have to go hunting for any of this. Once you accept the notice on first boot, the screen walks you through the three things that matter: WiFi, then your location, then your CGM. It puts up one card at a time and each card opens the right screen when you tap it. Every card has a Skip setup button that ends the walkthrough for good, and any step you have already finished is passed over, so it ends as soon as the device is ready. It only appears after a fresh install or a device reset, and each card says so. (needs firmware newer than v0.16.3)
-
Step 1 · about 5 min
Flash the firmware
Plug the device into your computer with a USB-C data cable and use the browser flasher on the build page. If you bought an assembled unit it is already flashed, so skip to step 2.
-
Step 2 · about 2 min
Join your WiFi
On the device: gear icon, then WiFi Setup. Networks scan automatically. Tap yours, type the password on the on-screen keyboard, and connect. More on WiFi.
-
Step 3 · about 2 min
Pick your CGM and sign in
Gear icon, then CGM Settings, then choose Dexcom Share, LibreLinkUp or Nightscout and enter your credentials. Each one has something to arrange on the phone side first: see CGM setup.
-
Step 4 · about 1 min
Set your location
Gear icon, then Time / Weather, then Search Location. Type a city or postal code and confirm. Timezone, weather and sunrise and sunset all follow from this.
-
Step 5 · about 90 sec
Wait for the first reading
Back on the home screen the arc around the trend arrow fills, then your number appears. CYGM checks for new CGM data every 90 seconds from then on. That is it. Next, set your alarms.
Total: about ten minutes
Everything you enter is stored locally on the device and used only to talk to your provider. There is no CYGM account and no server of mine in the path. If you give a device away, sell it, recycle it or throw it out, run Erase device first to remove the saved credentials. More on where your data goes.
02 Home screen
Home screen
Two cards. Time and weather on the left, glucose on the right. This is the screen the device sits on all day, and it is built to be read from across a room.
Swipe for more
Reading the glucose card
- The big number is your most recent reading. Its colour tracks your own alarm thresholds: green in range, yellow approaching a warning, red past an alarm.
- Under it the signed delta, for example +17, is the change since the previous reading, and the time-ago line tells you how fresh it is: "Just now", "1 min ago", and so on.
- The trend arrow glows and rotates smoothly to its new angle whenever the direction changes, so a change catches your eye without you staring at the screen.
- A rapid rise or fall is drawn differently: two red arrows side by side that slide and pulse. That is a built-in visual alert and it fires on the trend alone, independent of your threshold alarms.
- The semicircle arc around the arrow counts down to the next check. It is full right after a check, drains as the seconds pass, sits empty when the next check is due, and turns blue while the device is actually fetching.
- If a reading goes stale, the number greys out with a strikethrough and the age is shown, so an old value is not easily mistaken for a current one.
- Along the top of the card: battery with percentage, the bulb icon for the display sheet, and the gear icon for settings.
CYGM checks for new CGM data every 90 seconds, but how often a genuinely new value appears is decided by your CGM system and its cloud service, not by the device. A Dexcom sensor typically produces a reading every five minutes; current Libre systems may produce one every minute. Most checks simply find the value that was already there, and the time-ago figure keeps counting up until a fresh one lands.
The time and weather card
- Current time and the full date.
- Weather icon and condition, current temperature, and today's high and low.
- Your location name.
- Sunrise and sunset times along the bottom.
Gestures
-
Swipe left on the glucose card
Expands to the big-number view. The best setting for a nightstand or a kitchen counter.
-
Swipe right
Collapses back to the two-card layout.
-
Tap the trend arrow
Opens the glucose chart.
-
Double-tap a dimmed screen
Wakes it. The first tap only wakes, it never presses whatever was underneath.
03 Glucose chart
Glucose chart
Tap the trend arrow on the home screen and the history opens full-screen. This is where a number becomes a pattern.
- Pick a window with the tabs across the top, or swipe left and right on the chart to move between them. 1h3h6h12h24h
- Tap any point on the line to inspect that exact reading, value and time.
- The line is coloured by value, and the shaded band shows your configured range, defined by your low and high warning thresholds.
- The statistics bar along the bottom summarises the visible window.
- Tap Close to return to the home screen.
What the statistics mean
| Stat | Meaning |
|---|---|
| Low | Lowest reading in the window. |
| Avg | Average of every reading in the window. |
| High | Highest reading in the window. |
| Configured range | The percentage of readings between your configured low and high warning thresholds. This is not clinical Time in Range, which is measured against a standard 70 to 180 mg/dL target rather than your own settings. Move a threshold and this number moves with it. |
| GMI | Glucose Management Indicator, a calculated value that approximates A1C from average glucose. It may differ from a laboratory A1C. Normally read over about 14 days; see the caution below. |
| CV | Coefficient of variation, a measure of glucose variability. The device flags values above 36%, the commonly used clinical target being 36% or below. Normally read over about 14 days; see the caution below. |
Both are normally interpreted over about 14 days of data. Over a window of 1 to 24 hours they describe only what you are looking at, and they are not comparable with the GMI or CV on a standard 14-day report from your CGM software.
All of these statistics describe only the window you are looking at, and only the readings the device managed to collect. They are a quick read, not a clinical report. Use your provider's own app for anything you plan to act on.
04 Settings menu
Settings menu
Tap the gear icon on the home screen. Everything configurable lives behind one of these four rows or the two icons in the title bar.
- CGM Settings chooses your data source and signs you in. Details.
- WiFi Setup scans, joins and manages saved networks. Details.
- Time / Weather holds location, timezone and how often weather refreshes. Details.
- Alarms holds the four glucose alarm tiers and, behind the gear in that screen's title bar, the alert options.
- The question mark in the title bar opens About: firmware version, Check for Updates, the SD logging checkbox, and Erase device.
- The red power icon powers the device off. You hold a confirm button to complete it, so a stray tap cannot shut you down.
Erase device wipes stored settings: WiFi credentials, CGM login, alarms, location, everything. It is not a troubleshooting first step, and you will have to run the whole quick start again afterwards.
Always run it before a device leaves your hands. Giving one away, selling it, sending it for repair, recycling it or throwing it out all leave your WiFi password and CGM login on the board unless you erase them first. It does not touch a microSD card, so remove the card or wipe it separately.
05 CGM setup
CGM setup
The device does not read your sensor directly. It reads the sharing service your sensor already publishes to.
Pick the one that matches your setup. Each has something to arrange on the phone side first: CYGM lets you see glucose without reaching for your phone, but with Dexcom Share and LibreLinkUp the wearer's own app or receiver still has to be uploading to the provider's cloud for there to be anything to read.
Dexcom Share
The device signs in as a follower on your Dexcom Share account and reads the same stream your followers see. Compatibility: G6 and G7 through Dexcom Share. Other Share-enabled Dexcom systems may work, but they have not been tested.
Before you start, on your phone
- Share must be turned on in the Dexcom app.
- There must be at least one follower on the account. Share stops publishing entirely when the follower list is empty, so if you have none, invite yourself or a family member.
On the device
- Gear, then CGM Settings, then Dexcom Share.
- Tap the Username field and type the username you use to sign in to the Dexcom app.
- Tap the Password field and enter your password. The eye icon reveals what you typed if a character went astray.
- Submit. A progress indicator runs while the device authenticates, then a success banner appears and readings start arriving.
Sign in with the account's own username and password, not a follower's. The device is the follower.
LibreLinkUp
The device connects through LibreLinkUp, the follower app for FreeStyle Libre sensors. You need a working LibreLinkUp account that already shows readings before you type anything into the device.
Compatibility: any sensor that reports into LibreLinkUp, confirmed with Libre 2 and Libre 3. If your sensor shows up in the LibreLinkUp app, the device can read it.
First, set up LibreLinkUp on your phone
What you need:
- A FreeStyle Libre sensor that reports into LibreLinkUp, confirmed with Libre 2 and Libre 3.
- The FreeStyle Libre app on the sensor wearer's phone.
- The LibreLinkUp app installed on a phone, yours or the wearer's.
Step A, the sensor wearer sends an invitation. On the phone paired with the sensor:
- Open the FreeStyle Libre app.
- Open the menu at the top left and go to Connected Apps, labelled Share in some versions.
- Under LibreLinkUp, tap Manage or Connect.
- Tap Add Connection.
- Enter the name and email address of the person who will sign in on the device.
- Tap Add. An invitation email goes out.
Step B, accept it and create the account.
- Open the LibreLinkUp invitation in your email.
- Install LibreLinkUp from the link if you do not have it.
- Open the app, tap Get Started, and accept the licence agreement.
- Create your account: country, name, email, password.
- Verify the account from the confirmation email.
- Sign in and accept the sharing invitation.
Once you can see live readings in the LibreLinkUp app, the account is ready. Use that same email and password on the device. Following yourself? Invite your own email address in step A. You end up with a LibreLinkUp account that follows your own sensor.
On the device
- Gear, then CGM Settings, then LibreLinkUp.
- Enter the email and password of your LibreLinkUp account.
- Submit. On success a banner confirms it and readings begin flowing.
LibreLinkUp accounts are region-locked. Your account has to be in the same country or region as the sensor wearer's, or the sharing link simply will not resolve.
Nightscout
If you run your own Nightscout site, the device reads from it directly. Nightscout is not a CGM in its own right, it is a data source you host, so the compatibility question is simply: any CGM already supported by your Nightscout setup. Nightscout has already done the normalising by the time the device sees it.
First, create a read-only access token
Do this before you touch the device. CYGM only ever reads from Nightscout, so give it a token that can do nothing else.
- Open your Nightscout site and go to Admin Tools, under the hamburger menu.
- Under Subjects, People, Devices, etc., add a new subject. Name it something you will recognise later, such as cygm.
- Give it the readable role and nothing more. That role grants read access to your entries and no ability to write, edit or administer.
- Save. Nightscout generates an access token for that subject, a string like cygm-a1b2c3d4e5f6. Copy it.
The device authenticates with the access token only, and a readable token limits what a lost or stolen device could ever do.
Also have ready
- Your Nightscout site must be reachable over the internet and currently receiving data.
- The site URL, including https:// and with no trailing slash.
On the device
- Gear, then CGM Settings, then Nightscout.
- Enter the site URL.
- Enter the access token you created above.
- Submit. On success readings begin flowing.
Typos in the URL are the most common failure here. A trailing slash or a missing https:// is enough to break it.
If your site uses a self-signed certificate
The device checks the identity of every site it connects to, and a self-signed certificate cannot be checked. Sign-in will fail and the device will say so: the server could not be reached securely. This is deliberate. A connection that cannot be verified is one that something on the network can read or alter, and glucose readings are not worth that risk over the open internet.
Two ways forward. Give the site a certificate from a public authority; Let's Encrypt issues them free, and most reverse proxies will obtain and renew one for you. Or, if the site lives on the same network as the device and never leaves it, type the address with http:// at the front. That is an explicit choice to skip encryption on your own network, and the device will honour it rather than pretend to be secure. Typing https:// against a site that only speaks plain HTTP fails the same way, because the device really does try to negotiate a secure connection first.
06 WiFi
WiFi
The device needs WiFi for glucose data, weather, time sync and updates. There is no cellular fallback, so if the network is down, readings stop until it comes back.
- Open gear, then WiFi Setup. The device scans automatically as soon as the screen opens.
- Tap the refresh icon in the title bar to scan again if your network has not appeared yet.
- Tap a network name, then type the password on the on-screen keyboard. The keyboard supports shift for one character and caps lock by tapping shift twice, and the eye icon reveals the password.
- Connect. A progress overlay reports what is happening, and the network gets a green dot once it is saved.
- To forget a saved network, tap the red cross next to it.
The radio in this device cannot see 5 GHz networks. If your router publishes both bands under one name the device will still find the 2.4 GHz half, but a 5 GHz-only network will never show up in the scan list no matter how many times you refresh.
07 Time and weather
Time and weather
One setting drives most of this screen: your location. Set it and the timezone, forecast and sunrise and sunset all follow.
- Open gear, then Time / Weather.
- Tap Search Location and type a city name or postal code. Results narrow as you type; confirm the one you want.
- The timezone is derived from that location automatically, and the clock syncs over the network. You do not pick it separately.
- Choose a weather update interval: 15 min30 min1 hr Longer intervals mean fewer network wake-ups, which matters on battery.
If the device cannot reach the lookup service it falls back to a built-in list, so you can still set a sensible location before WiFi is sorted out.
Clock format, date format and glucose units
The device supports both 12-hour and 24-hour clocks, alternate date formats, and both mg/dL and mmol/L for glucose. These follow your regional settings rather than needing to be picked one at a time. Set the region correctly and the whole interface, including the alarm thresholds and the chart, speaks in your units.
08 Display and night dim
Display and night dim
Tap the bulb icon on the home screen. A two-page sheet slides up: brightness on page one, the night schedule on page two. It closes itself after about 30 seconds if you walk away.
Swipe for more
Brightness and charging behaviour
- Drag the brightness slider. The screen responds immediately, so you can set it by eye in the room you are actually in.
- Dim when plugged in is off by default, meaning that on USB power the screen simply stays on. That is the intended way to run the device: plugged in, always readable, no waking it up to check a number.
- Turn that toggle on if you want the screen to dim on charge too, which is useful in a bedroom where the device is plugged in overnight.
Night dim and the night face
- Turn on Night Dim and set a start and an end time.
- Pick a night level: 5%15%30%
- Inside that window the screen drops to the level you chose and hands the whole display to one huge glucose number, coloured by zone: green in range, amber near a warning, red at an alarm, with the trend arrow beside it.
- The time moves to a small white readout in the top bar. That is deliberate: at a sleepy 3am glance a big clock and a big glucose value look alike. At night only one number is big, and it is the one that matters.
- The dimmed bulb icon stays in the top corner all night, so the display settings are always one tap away.
- Outside the window everything returns to the layout and brightness you had before.
Dimming and waking
- On battery the screen dims on its own after roughly two minutes of no touches.
- Double-tap anywhere to wake it. The first tap only wakes the screen, it never activates whatever button happened to be under your finger, so you cannot snooze an alarm or open a menu by accident.
- The BOOT button on the board also wakes the device, which is handy in the dark.
09 Alarms
Alarms
Four tiers, each configured independently: High Alarm, High Warning, Low Warning and Low Alarm. Warnings are the early nudge; alarms are the ones that mean now.
Swipe for more
Configuring a tier
- Open gear, then Alarms and tap the tier you want to change.
- Drag the threshold slider to the value that should trigger it. Tapping the number itself opens a keypad, so you can type the exact value instead of hunting for it with the slider. (needs firmware newer than v0.16.3)
- Audio Alert turns sound on and exposes the tone and a volume slider.
- Keep Sounding decides whether that tier's tone ever pauses. Every alarm repeats until you answer it; left off, the tone rests after three minutes and comes back two readings later, and switched on it never pauses at all. It sits on the tier's own page and replaced the old Repeat switch. (needs firmware newer than v0.16.3)
- Screen Flash flashes the display and LED Flash flashes the on-board LED. Either works on its own if you need a silent alert.
- Back on the Alarms list, the range bar across the bottom shows all four thresholds together, which is a fast way to catch an overlap or a gap you did not intend.
Threshold colours on the home screen and the target band on the chart are both driven by these numbers. Change a threshold and the rest of the interface follows.
Sound comes from the board's amplified speaker output, with an optional speaker wired to it. If your unit was built without one there is nothing to hear, so use Screen Flash and LED Flash instead. Either works on its own.
Choosing a tone
- 28 tones spread across seven pages, grouped from gentle chimes through to genuinely alarming sirens.
- Tap the green play button to preview any tone without selecting it.
- Random (Loud) is the interesting one. Instead of a fixed melody it plays a fresh, unpredictable loud sequence every time. Familiar alarms tend to fade into the background after a few weeks; a sequence you have not heard before is designed to reduce that habituation.
When an alarm fires
The device takes over the whole screen: the glucose value at full size, a plain statement of why it fired, and two buttons.
- SNOOZE silences it for your configured snooze length. If glucose is still out of range when that expires, it fires again.
- DISMISS is a hold, not a tap. Deliberately harder, so a half-asleep tap is unlikely to clear a genuine low.
- The BOOT button snoozes without needing to find the right part of the screen. Useful in the dark.
- Nobody home? If the alarm goes completely untouched for 30 minutes it stands down on its own and the display returns to the home screen. It counts as a snooze, never a dismiss: if the reading is still out of range when the snooze window ends, the alarm fires again. (v0.15.2 and later for the full-screen takeover, extended to tone-only alarms in v0.15.3)
- You can turn auto-snooze off on the unattended page of alert options. The control takes a three-second hold, so a stray tap cannot flip it. (v0.15.3 and later)
An urgent low at 55 mg/dL plays at full volume regardless of your settings. It cannot be turned off, and it overrides snooze, quiet hours and mute. Alarms normally hush after three minutes and return two readings later, but the safety floor ships with Keep Sounding switched on, so its tone does not pause at all. See alert options.
10 Alert options
Alert options
Tap the gear icon in the Alarms title bar for six pages of behaviour settings that apply across all four tiers. This is where alarms stop being a threshold and start being a system you can live with.
Quiet hours and snooze
- Quiet Hours defines a window in which non-urgent alerts go visual-only: screen and LED still tell you, the speaker stays silent. Set a start and an end.
- Snooze default sets how long the SNOOZE button buys you when an alarm fires.
Escalating volume
An alarm that is ignored gets louder over time instead of droning at one level. It starts polite and keeps climbing, which is designed to be hard to miss without making every alert shout from the first second.
Data-gap alert
Warns you when readings stop arriving, the silent failure a threshold alarm can never catch, because a device with no data has nothing to compare against a threshold. When it fires it also suggests likely causes, so you know where to start looking: the WiFi, the sensor, or the sharing service. It is a starting point, not a diagnosis.
Predictive low warning
Projects the current rate of change forward and can warn up to roughly 20 minutes before the trend is projected to cross your low threshold. It is a projection from the current trend, so it can be early, late or wrong if the trend turns. Treat it as a head start, not a forecast.
Rate-of-change alert
Fires on how fast glucose is moving rather than where it currently sits. A steep fall from a perfectly normal number is worth knowing about before it becomes a low.
Urgent-low safety floor
This one is not a preference. It cannot be disabled, turned down or scheduled around, and it breaks through snooze, quiet hours and mute. Every other alert on this page can be tuned to taste; this is the floor underneath all of them, and it is deliberately not yours to move.
Every other tier hushes after three minutes and returns two readings later unless you give it Keep Sounding on its own alarm page. This one ships with Keep Sounding on, so it does not stop until someone answers it. Its switch is the one on the Safety Floor page here, and you can turn it off, but think hard before you do.
Unattended auto-snooze
The sixth page controls what happens when an alarm rings into an empty room. With auto-snooze ON, the default, an alarm nobody touches for 30 minutes snoozes itself, screen and tone both, and re-fires if glucose is still out of range when the snooze ends. With it OFF, an unattended alarm keeps sounding until someone responds. The auto-snooze behaviour itself arrived in v0.15.2 for the full-screen takeover; v0.15.3 added this page and extended auto-snooze to tone-only alarms.
- Changing it takes a three-second hold on the ON/OFF control, with a progress fill so you can see the hold registering. A tap does nothing, deliberately. This is a safety behaviour, not a preference to toggle in passing.
- Which setting suits you depends on your household. Auto-snooze keeps a bedside device from flashing and sounding all night at nobody, while OFF makes more sense if a ringing alarm is meant to bring someone in from another room.
11 Updates
Updates
The device updates itself over WiFi. No cable, no computer, and your settings survive the process.
- The device checks for updates automatically once a day in the background. If one is waiting, it tells you.
- To check by hand: gear, then the question mark (About), then Check for Updates. The check runs in the background with a progress overlay, so the screen stays usable.
- If an update is available you will see the new version and an install option.
- The device downloads and installs over WiFi, then reboots into the new firmware.
- Your settings are preserved: WiFi, CGM login, alarms, location, display preferences. An update replaces the firmware, not your configuration.
- After the reboot the home screen shows a one-time What's New card with the new version number and a short list of what changed. Tap OK and it is gone; it never interrupts an alarm or the night face. (v0.16.0 and later)
The device keeps two firmware slots and is designed to fall back to the previous firmware if an update is interrupted, then reboot into it. Reconnect and try again.
12 Battery and power
Battery and power
The battery is optional. Plenty of people run the device permanently plugged in on a desk or a mantle. That is the intended setup, and the screen stays on for it.
- With an optional LiPo battery fitted, the top of the glucose card shows a battery icon and percentage. Tap the battery to show or hide the percentage; the choice is remembered.
- While charging, the battery icon animates so you can tell at a glance that the cable is actually delivering power.
- With no battery fitted the device notices and shows a small plug icon in that spot instead of a gauge: no percentage, no low-battery beeps, no shutdown. (v0.16.2 and later)
- At 10% the device beeps to warn you.
- If it keeps draining, the device shuts itself down rather than running the cell flat. Deep discharge is what kills a LiPo permanently.
- On USB power the screen stays on by default. Change that under display if you would rather it dimmed while charging.
- To power off deliberately: gear, then the red power icon, then hold the confirm button.
If you are storing the device unused for a long stretch, charge it first. A powered-off unit still draws a trickle, and a LiPo left flat for months may not come back.
13 SD card logging
SD card logging
Optional, and controlled by a card: with no microSD card in the slot nothing is written. Put a card in and the device keeps its own copy of every reading it receives, unless you switch that off.
- Insert a microSD card. One fitted while the device is running is picked up on the next reading cycle, usually inside two minutes, so there is no need to restart.
- Open gear, then the question mark (About). The Save CGM data to SD checkbox appears there once a card is present, and it starts ticked.
- Leave it ticked and every reading is appended to a CSV file on the card. Untick it to stop logging.
- Pull the card and open the CSV in any spreadsheet program. It is plain text, no special software involved.
- Or drop the files into the card viewer, which turns them into charts, time in range and a printable report for a clinic visit. It runs entirely in your browser, nothing is uploaded, and it will read the card straight off the device over the USB cable if you would rather not take it out.
A card inserted while the device is running is found on its own, usually inside two minutes. There is no need to restart it.
14 Tips and tricks
Tips and tricks
The things that are not obvious from the screens themselves, mostly learned by living with the device rather than by designing it.
-
Double-tap to wake
Two taps anywhere on a dimmed screen. The first tap only wakes it, so you can tap confidently in the dark without hitting something.
-
Swipe for the big number
Swipe left on the glucose card for the across-the-room view, and right to come back. This is the setting most people leave it on overnight.
-
Tap chart points
Every point on the chart is tappable. Instead of guessing at the line, tap it and read the exact value and time.
-
Use Random (Loud)
A different sequence every time, designed to reduce the habituation that makes a familiar alarm easy to sleep through. Worth it for the alarms that genuinely matter.
-
Set quiet hours for the night
Warnings go visual-only overnight while the urgent-low safety floor still sounds at full volume. Fewer wake-ups, without silencing the one that counts.
-
Night dim for bedrooms
Schedule it, pick 5%, and the screen becomes one dim zone-coloured glucose number that does not light the room, with the time small up top where it is hard to mistake for the glucose value.
-
Read the trend arrow
The arrow is drawn as a solid head with a trail fading out behind it, so which way your glucose is moving reads from across the room. A second arrow appears alongside it when glucose is moving fastest. CYGM checks about every 90 seconds; whether a check finds a new value is up to your CGM service. No need to keep refreshing anything.
-
Leave it plugged in
On USB power the screen stays on by default. That is the whole point of a dedicated display: glance, do not unlock.
-
The BOOT button snoozes
When an alarm fires you can snooze with the physical button, without finding the right spot on the screen. Handy at 3am.
-
mmol/L is supported
Glucose units follow your regional settings. Set the region and the number, the thresholds and the chart all switch together.
-
Location search works offline
There is a built-in fallback list, so you can set a location before the network is sorted out.
-
Log to SD for history
Drop in a microSD card and tick the box in About. You get a plain CSV of every reading, readable in any spreadsheet.
15 Troubleshooting
Troubleshooting
Find the symptom, read the likely cause, apply the fix. Work down each list. They are ordered by how often each cause turns out to be the real one.
Screen stays black
- The screen is dimmed, not off
- Double-tap the screen. On battery the display dims after about two minutes of inactivity, and one tap is deliberately ignored so you cannot press something by accident. If night dim is scheduled, you may also simply be inside that window.
- No power
- Plug into USB with a cable you know carries data and power, not a charge-only cable. If a battery is fitted and fully drained, give it several minutes on the charger before expecting anything on screen.
- The device powered itself off
- Press the BOOT button on the board to wake it. The device shuts down on its own when the battery gets critically low, which is protection, not a fault.
- Brightness set to zero
- If you can see faint content at an angle, the backlight is just very low. Tap the bulb icon and raise the brightness slider.
WiFi is connected but no readings arrive
WiFi being up only proves the device can reach the internet. The break is almost always between your sharing service and the device's login. Check the cause that matches your provider.
- Dexcom Share: share is off, or there are no followers
- Open the Dexcom app and confirm Share is enabled and that at least one follower exists. With an empty follower list, Share publishes nothing at all and the device has nothing to read. Adding any follower restores the stream.
- LibreLinkUp: sharing was never set up, or the region does not match
- Open the LibreLinkUp app on your phone. If it does not show live readings, the device cannot either, so fix it there first by completing the invitation flow in CGM setup. Also confirm your LibreLinkUp account is in the same region as the sensor wearer's.
- Nightscout: wrong URL or token
- Re-enter the site URL exactly, including https:// and with no trailing slash, and re-enter the access token. The device authenticates with a token, not an API secret, so if you pasted a secret, create a readable token in Admin Tools instead. Confirm the site loads in a browser and is currently receiving data from your uploader.
- The sensor itself is in warm-up or has ended
- Nothing to fix on the device. During sensor warm-up or after a session ends there is no data to share. Readings resume on their own.
- Password changed
- If you changed your provider password, re-enter it under gear, then CGM Settings. The device is signing in with the old one.
Turn on the data-gap alert and the device will tell you when readings stop and suggest likely causes, rather than leaving you to notice a stale number.
Flashing fails, or the computer does not see the device
- Charge-only USB cable
- Use a cable you know carries data. This is by far the most common cause, and the symptom, a device that powers on but never appears, looks exactly like a broken board.
- Missing USB-to-serial driver
- Install the USB serial driver for your operating system, then unplug and replug the device. Until the driver is present, no serial port appears for the flasher to select.
- The board is not in bootloader mode
- Hold the BOOT button while you plug the cable in, or while starting the flash, then release. Some boards need this every time.
- Another program holds the serial port
- Close any serial monitor, terminal or IDE that might have the port open, then retry. Only one program can hold a serial port at a time.
- Unsupported browser
- Browser flashing needs a Chromium-based desktop browser with Web Serial. It does not work on phones or tablets. Full instructions live on the build page.
An alarm did not make any sound
- No speaker is fitted
- Audio comes out of the board's amplified speaker output, and the speaker itself is optional. If your unit was built without one, no setting will produce sound, so turn on Screen Flash and LED Flash for the tiers you care about.
- Volume is low, or audio is off for that tier
- Open gear, then Alarms, tap that tier, and check that Audio Alert is on and the volume slider is not near the bottom. Volume is per tier, so a quiet warning does not mean a quiet alarm.
- Quiet hours is active
- That is quiet hours doing its job: non-urgent alerts go visual-only inside the window. Adjust the window under alert options if it is catching more than you intended.
- The alarm is snoozed
- A snoozed alarm stays silent until the snooze expires, then re-fires if glucose is still out of range. Shorten the default snooze length in alert options if it is too generous.
- The tier is switched off, or the threshold was never crossed
- Confirm the tier's toggle is on and look at the range bar at the bottom of the Alarms screen. A threshold set further out than you remember is a common surprise.
- A quiet tone choice
- Preview tones with the play button and pick something with more presence. For the alarms that matter, Random (Loud) is the one designed not to be tuned out.
An urgent low at 55 mg/dL sounds at full volume regardless of every setting above. If that was silent, treat it as a hardware fault and get in touch.
Touch is not responding
- The screen is dimmed and you have only tapped once
- Double-tap. A single tap on a dimmed screen wakes nothing on purpose, so it can look like touch is dead when the device is working perfectly.
- The touch controller has stopped responding
- Wait a few seconds. The device watches its own touch controller and reboots itself within seconds if it stops answering. You will see it restart and come back on its own.
- It keeps rebooting
- Repeated reboots usually mean a loose touch ribbon connector rather than software. Power down, reseat the ribbon at the display connector, and power back up.
- A screen protector or wet fingers
- The panel is capacitive. A thick film over it, or moisture on the glass, degrades touch. Wipe the screen dry and try again.
The time or weather is wrong
- No location set, or the wrong one
- Gear, then Time / Weather, then Search Location. Timezone and weather both derive from the location, so a wrong city gives you both a wrong clock and a wrong forecast. Watch for same-named towns in other states and confirm the right match.
- The clock has not synced yet
- The device sets its clock over the network shortly after connecting. Confirm WiFi is up and give it a minute after a reboot.
- A daylight-saving change just happened
- Re-confirm your location so the timezone rules are re-applied, then let the clock re-sync.
- Weather looks stale
- Check your weather update interval. On a 1 hr interval the reading on screen can legitimately be nearly an hour old. Drop it to 15 min if you want it fresher.
- The offline fallback was used
- If you set your location while offline, the built-in fallback may have picked a nearby entry rather than an exact one. Search again once you are online for a precise match.
16 Common questions
Common questions
Can I make treatment decisions from CYGM?
No. CYGM is an open-source, experimental secondary CGM display. It shows data your existing CGM system has already produced. It is not FDA-cleared or FDA-approved, and it has not been clinically validated.
Do not use CYGM as the sole basis for a treatment decision, and do not treat it as a replacement for your prescribed CGM receiver or app and the alerts they provide. Always confirm glucose information on your official CGM system before dosing or treating.
Readings here can be delayed, stale or missing entirely if a network, a sharing service or the sensor itself has a problem, and the device cannot always tell you which.
I built it as a father, to keep an eye on my daughter's numbers from across a room. That is exactly what it is good for, alongside the equipment your care team prescribed and never instead of it.
Does my glucose data pass through your servers?
No. The device talks directly to your provider's API: Dexcom Share, LibreLinkUp, or your own Nightscout site. Your readings never travel through anything of mine.
There is no CYGM account. Nothing to sign up for, no profile, no cloud copy of your data. The credentials you type are stored locally on the device, in its own flash memory, and are used only to sign in to the service you chose.
Before a device leaves your hands, whether given away, sold, sent for repair, recycled or thrown out, run Erase device from the About screen. That is what clears the stored WiFi password and CGM login. A device that is simply powered off still has them on the board. A microSD card is not erased, so remove it or wipe it separately.
The device does reach out for two other things: the weather for the location you set, and a once-a-day check for a firmware update. Neither carries your glucose data.
How long does the battery last?
It depends almost entirely on brightness and how often the screen is awake, so there is no single honest number to quote. A device left at full brightness with the screen permanently on drains quickly; one that dims after two minutes and uses night dim overnight lasts substantially longer.
The battery is optional and mainly there for portability. The intended setup is plugged in: on USB power the screen stays on by default, which is the whole point of a dedicated display. Use display to trade brightness for runtime if you do run it on battery.
Can I run more than one device on the same account?
Yes. Each device signs in independently, so you can put one in the kitchen and one in a bedroom, both following the same CGM account. Set each one up with the same CGM setup steps.
Alarms, thresholds, brightness and night dim are stored per device, so the bedroom unit can be quiet and dim while the kitchen unit is loud and bright. That is usually what you want.
How often does the firmware get updated?
Irregularly, and by one person. Updates land when a fix or a feature is actually ready rather than on a schedule. The device checks once a day on its own, so you do not need to watch for them.
Updates install over WiFi and preserve your settings, as described under updates. Release notes for each version are published on the site.
Written for firmware v1.1.10 Release
CYGM is an open-source, experimental secondary CGM display. It is not FDA-cleared or FDA-approved, and it has not been clinically validated. It shows readings that have already travelled through your own CGM's app and cloud service, so it can lag, gap or fail independently of them.
Never use it as the sole basis for a treatment decision, and never rely on it as your only alarm. Always confirm on your prescribed CGM receiver or app before dosing or treating.