Up to 3 uses are the normal use period for the sticky sensor behind the ear. If it is not secure at the time you go to bed, then you will not have a good contact and will not receive the full value of the sleep tones through the night for your recovery in deep sleep.
Do not use each SmartSleep sensor more than 3 nights because it could affect device performance. The SmartSleep Sensor (behind the ear) is considered a disposable component and should be replaced every 3 nights.
The gel in the middle of the SmartSleep Sensor is very important to its function. If the gel becomes dislodged, discard the sensor and use a new one.