| Warm-Up Period | 60 minutes (Libre 2 & 3) |
| Max Scan Distance | 4 cm (1.5 inches) |
| Sensor Wear Duration | 14 days (Libre 2), 14 days (Libre 3) |
| Water Resistance | IP27 — 1m depth, 30 minutes max |
| Transmission Method | NFC (Libre 2 scan), Bluetooth (Libre 3 auto) |
| Abbott Support (UK) | 0800 170 1177 |
Key Takeaways
- Most FreeStyle Libre reading failures are caused by poor skin contact, sensor warm-up periods, or interference from scanning distance.
- Sensors have a 60-minute warm-up period after application before readings begin.
- Scanning too far away (>4cm) or through thick clothing can block NFC communication.
- A failed sensor can be replaced free of charge by contacting Abbott support.
Why Is My FreeStyle Libre Sensor Not Reading?
The FreeStyle Libre system uses Near Field Communication (NFC) technology to transmit glucose data from the sensor to the reader or smartphone. When a reading fails, it is almost always due to one of a handful of identifiable causes.
Common Causes and Fixes
1. Sensor Still in Warm-Up Mode
After applying a new sensor, the FreeStyle Libre 2 and 3 require a 60-minute warm-up period. During this time, no readings are possible. Wait the full hour before attempting your first scan.
2. Incorrect Scanning Technique
Hold your reader or smartphone within 4 cm (1.5 inches) of the sensor. Scan slowly and steadily — moving too fast interrupts NFC communication. Remove bulky cases from your phone that may block the NFC antenna.
3. Sensor Placement Issues
Sensors should be placed on the back of the upper arm, on soft tissue. Avoid areas over bone, muscle, or scar tissue. Poor adhesion due to oily or damp skin at application time is a leading cause of early sensor failure.
4. Sensor Knocked or Lifted
If the sensor has been hit, pulled partially off, or exposed to excessive moisture, the filament may have shifted. Check that the sensor sits flush against the skin. Using a sensor armband or overtape patch from MDS Diabetes can significantly improve adhesion and protect against accidental dislodgement.
5. Signal Interference
Hospital MRI machines, strong electromagnetic fields, and even some sleep positions (lying directly on the sensor) can temporarily block readings. Move away from the interference source and retry.
6. Low Phone Battery or NFC Disabled
Ensure your smartphone's NFC is enabled in settings and the battery is above 15%. Some Android devices disable NFC in low-power mode.
Sensor Error Codes Explained
| Error Message | Meaning | Action |
|---|---|---|
| Sensor Warm-Up | New sensor initialising | Wait 60 minutes |
| Sensor Error | Sensor malfunction detected | Contact Abbott for replacement |
| Sensor Expired | 14-day wear period ended (Libre 2) | Apply a new sensor |
| No Sensor Found | NFC scan failed | Retry scan, check distance |
When to Contact Abbott
If you have ruled out all of the above causes and the sensor still fails to read, contact Abbott Diabetes Care at 0800 170 1177 (UK). Abbott routinely replaces failed sensors at no cost. Have your sensor lot number ready.
Preventing Future Failures
- Clean and dry the application site with an alcohol wipe; allow to dry fully before applying.
- Press and hold the applicator firmly for 5 full seconds on application.
- Protect the sensor with an overtape patch or dedicated armband — available at mdsdiabetes.com.
- Avoid submerging the sensor beyond 1 metre or for longer than 30 minutes.
FreeStyle Libre 2 vs Libre 3 Reading Differences
The Libre 3 sends readings automatically every minute to a smartphone via Bluetooth — no scanning required. If readings stop on Libre 3, check Bluetooth is active and the LibreLink app is running in the background. The Libre 2 still requires a manual scan every 8 hours to prevent data gaps.