Therefore, the 9V signal is then lowered once more using a voltage divider circuit. When the PIR sensor is triggered, it activates the timer circuit. The timer circuit is driven by a 555 timer.

As an example, [Circuit Valley] has an IKEA Vallhorn motion sensor for a teardown, it’s as you might expect, a passive infrared sensor (PIR) sensor coupled with a Zigbee interface.

The sensor does have some limits. It can only detect motion up to about 16.5 feet away. And while Philips will give you the option of reducing that — that is, only turning on lights when motion ...