The presented schematic shows how to build a simple PIR motion sensor. PIR sensors allow motion sensing, it is almost always used to detect whether someone has moved in or out of the sensors range.

ICP DAS USA releases PIR-130-DC, a 1-channel passive infrared (PIR) sensor module that detects human-body generated infrared waves within a range of approximately 8 meters (315 inches) in diameter ...

It’s really hard to overstate how awesome ESP8266 development boards like the Wemos D1 Mini really are. For literally a couple of dollars you can get a decently powerful Wi-Fi enabled microcontroller ...