HC-SR501 PIR Motion Sensor

Trigger a light, a camera, or an alarm whenever a warm body moves nearby — pyroelectric sensors detect the heat signature, not visible motion.

Difficulty: Breadboard. Estimated build time: about 20 minutes. Estimated parts cost: about US$2.80. 5-part bill of materials with live supplier pricing. A motion-activated trigger that fires a digital HIGH whenever a warm body crosses the sensor's field of view.