PIR module usually requires an initial warm-up period for the sensing elements to come up to the operating mode. This usually takes not less than 30 seconds. So a 30 seconds delay is intentionally ...

Present consists of just a PIR sensor and Arduino in a 3D printed enclosure to snap onto your monitor.

The actual circuit is just a piece of perfboard, a large, old relay from Sparkfun, and a PIR sensor [Greg] picked up last year.