How do I set sensitivity and reduce false detections on the Smart Sensor Microwave?

This article applies to the zencontrol Smart Sensor Microwave version 5.10 and above. Other zencontrol sensors may behave differently, so this guidance, especially the sensitivity values, does not carry across to them.

It detects motion from reflected radio waves (Doppler) rather than body heat, so it reacts to things a PIR ignores. For how to set a sensitivity value, see How do I change the sensitivity on zencontrol sensors?.

Detection shape

The field is elliptical, reaching further along one axis than the other. Mounted close to a large reflective surface such as metal or a masonry wall, the field can reflect and travel along it, stretching detection in that direction. If a false-trigger source is to one side, rotating the sensor 45 or 90 degrees swings the long axis away from it, often clearing the trigger without losing coverage.

Sensitivity and range

Sensitivity sets the detection distance: the lower the sensitivity, the shorter the range.

• 0 - motion detection disabled.
• 1 - very short range, under ~0.5 m.
• 2 and up - scales up to the maximum range of 8 m (mounted at 2.7 m).

Use 20 or above for normal coverage. The 1 to 19 band is a tuning range for reducing persistent false-triggering, but it cuts the detection distance drastically, so treat it as a last resort and walk-test the area afterwards: the shortened range may no longer reach everywhere it needs to.

Common causes of false detections

• Penetration - radio waves pass through glass, plasterboard and thin partitions, so the sensor can detect the next room or corridor.
• Reflective metal - large metal, pipes, ducting and shutters redirect the field into areas you did not mean to cover. Metal mounted very close to the unit, especially directly in front of its face, is a common microwave issue and a frequent cause of false triggers; keep the area in front of and around the sensor clear of metal. An example of this could be a metal pipe directly infront of the sensor.
• Moving water and vibration - water flowing in pipes, and HVAC outlets, fans and exhausts, all read as motion.
• Wind-blown movement - curtains, blinds, foliage or hanging signs swaying in a draught are read as motion.

Fixing false detections

In order:

1. Identify and remove the source - find what is triggering the sensor (see Common causes above) and remove or reduce it where you can. For example, a metal pipe directly in front of the sensor face may mean the sensor has to be moved away from that position.
2. Reduce sensitivity - step it down from the default toward 20 (this shortens the detection distance).
3. Re-aim and relocate - if it still false-triggers at 20, rotate or tilt the sensor away from the source (see Detection shape), and move it away from thin partitions, metal, pipework and air outlets.
4. Go below 20 - only if it still triggers, drop into the 1 to 19 band to pull the range in further. This will require a walk test to confirm that range reaches everywhere it needs to.