This may be due to environmental influences detected by the sensor pads, such as wind, fan, air conditioner, mobile, vibrations. Perform a test which will detect the source of the movement that the device detects. 

For example, sources of wind such as: air conditioner, an open window or a fan; movements of a baby mobile (which can vibrate even if it's not turned on) walking around the bed area or an intercom placed near the bed with intense transmission levels. 

Solutions: Eliminate sources of wind, remove the mobile etc. 

After neutralising all environmental influences, perform the test again. If even after neutralising all of the environmental influences, the alarm does not go off within 20 seconds, perform the following: 

1. In the back of the sensor pads, reduce the sensitivity level to position 2 (on both sensor pads) and perform again the Performance Test. If the alarm sounds within 20 seconds, than keep this sensitivity level. 
2. If the alarm does not go off in time, than reduce the sensitivity level to position 1 and perform again the Performance Test. If the alarm sounds within 20 seconds, than keep this sensitivity level.
3. If the alarm does not go off in time at this level, than it is suggested using only one sensor pad with the sensitivity level adjusted on position 1. 
4. PAY ATTENTION: Should false alarms sound as a result of reduced sensitivity, than increase the level of sensitivity and perform the Performance Test.