PIR Motion Detector Sensor Module HC-SR501

The HC-SR501 senses motion the way a security light does, by picking up the change in infrared heat signature as a warm body moves through its Fresnel-lensed detection cone, rather than needing any reflected light or sound. Two onboard potentiometers let a builder tune both how sensitive the detector is and how long its output stays high after triggering, which makes it practical to dial in for a small room versus a long hallway without changing any code. A jumper on the board also switches between single-trigger and repeatable-trigger modes, giving extra control over whether the output resets immediately or keeps extending while motion continues. It is a mainstay of DIY security systems, automatic lighting projects, energy-saving occupancy switches, and smart-home builds where a simple yes-or-no motion signal is all a project needs.