Two quick questions about the HC-SR501 PIR Infrared Motion Sensor

Hello everybody :)

I have two questions about the quite popular HC-SR501 PIR Infrared Motion Sensor:

  • does the sensor reveal motion even if the person is behind a thin wall?

  • is it possible to hack the sensor in order to get a smaller sensing angle, maybe around 30 degrees? The angle with the original lens is around 120 degrees. I was wondering if would be possible to remove the lens and replace it maybe with a cone o something similar in order to get a more directional sensor

Tricka90: does the sensor reveal motion even if the person is behind a thin wall?

Fairly unlikely unless the "wall" is paper thin.

Tricka90: I was wondering if would be possible to remove the lens...

The lens is an integral part of the sensor, but you could try coning off the extremities of the sensor's view with something that reflects IR wavelengths.

This article explains how they work: https://en.wikipedia.org/wiki/Passive_infrared_sensor

  • does the sensor reveal motion even if the person is behind a thin wall?

No.

  • is it possible to hack the sensor in order to get a smaller sensing angle, maybe around 30 degrees?

Put it down the bottom of a tube.