flipnCGM

May 26, 2026 · View on GitHub

A Flipper Zero application that reads Abbott FreeStyle Libre continuous glucose monitor (CGM) sensor serial numbers via NFC and optionally logs them to the SD card.

Features

Read FreeStyle Libre 1, 2, and 3 sensor serial numbers over NFC (ISO 15693)
Displays the decoded 9-character ASCII serial and raw 8-byte UID
Audio feedback on scan (short chime on success, low beep on unrecognised tag)
Configurable SD card logging with ISO 8601 timestamps and UTC offset
Four log levels: Off, Error, Info, Debug
UTC offset persists across app restarts (/ext/apps_data/flipncgm/settings.ff)

Screenshots

Scanning	Result

Installation

Flipper App Catalog

Search for flipnCGM in the Flipper App Catalog and install directly from the Flipper Mobile App or lab.flipper.net.

Manual — pre-built FAP

Download flipncgm.fap from the latest release.
Copy it to /ext/apps/NFC/ on your Flipper's SD card.

Build from source

# Install ufbt (requires Python 3.8+)
pip install ufbt

# Clone and build
git clone https://github.com/darendarrow/flipnCGM.git
cd flipnCGM
ufbt          # produces dist/flipncgm.fap
ufbt launch   # build and sideload to a connected Flipper over USB

Usage

Open flipnCGM from the NFC apps menu.
Hold a FreeStyle Libre sensor to the back of the Flipper Zero.
The decoded serial number and raw UID are displayed on screen.
Press OK to dismiss the result and scan another sensor.
Press Back (short or long-press) to exit.

Logging

Button	Action
UP	Cycle log level: Off → Error → Info → Debug → Off
LEFT / RIGHT	Adjust UTC offset in 30-minute steps

Log level and UTC offset are shown on the scanning screen. The UTC offset is saved automatically and restored the next time the app is opened.

Log file: /ext/apps_data/flipncgm/flipncgm.log

2024-06-01 14:23:45-05:00 [INF] flipnCGM started
2024-06-01 14:23:52-05:00 [INF] CGM read OK - Serial: 0R8FDDJ8J  UID: E0:7A:00:C2:1C:C6:45:11
2024-06-01 14:24:01-05:00 [INF] Non-Libre ISO15693 tag - UID: E0:04:...
2024-06-01 14:24:10-05:00 [ERR] NFC poller error during activation
2024-06-01 14:24:15-05:00 [DBG] Tag detected (scan_enabled was true)

Log entries are appended; the file is never truncated by the app. Delete it manually via the Flipper file manager if it grows too large.

Technical details

Serial number decoding

FreeStyle Libre sensors use ISO 15693 NFC tags. The 8-byte UID encodes the human-readable serial number printed on the sensor packaging.

UID byte	Example	Meaning
0	`E0`	Fixed — ISO 15693 tag identifier
1	`7A`	Abbott Diabetes Care manufacturer code
2–7	variable	48-bit big-endian encoded serial

Bytes 2–7 are treated as a 48-bit big-endian integer. Nine groups of 5 bits (MSB-first) are extracted and each mapped through a 32-character alphabet that omits B, I, O, S to avoid visual ambiguity:

0123456789ACDEFGHJKLMNPQRTUVWXYZ

Settings file

/ext/apps_data/flipncgm/settings.ff is a standard FlipperFormat key-value file:

Filetype: flipnCGM Settings
Version: 1
UTC offset minutes: -300

Compatibility

Sensor	Tested
FreeStyle Libre 1	✅
FreeStyle Libre 2	✅
FreeStyle Libre 3	✅ (UID format identical)