PIR sensors allow you to sense motion, almost always used to detect whether a human has moved in or out of the sensors range. They are small,
HC-SR501 Pyroelectric Infrared PIR Motion Sensor
PIR Motion Detection Sensor HC-SR501 - Silicon TechnoLabs
Infrared Sensor with Control Circuit Board The Sensitivity and Holding Time Can be Adjusted Detection Distance: 3 to 7m (can be adjusted) Detection
PIR Motion Sensor Detector Module HC-SR501 - MechBlock
Tarjeta OpenScale - DynamoElectronics
PIR Sensor Human Body Detecting Module Pyroelectric Hc-Sr501
is a pyroelectric device that detects motion by measuring changes in the infra
PIR Motion Sensor HC-SR501 Motion Detector Pyroelectric Infrared Module
Pir Motion Sensor Detector Module Hc Sr501 at Rs 50/piece in Thane
Sensor de movimiento PIR HC-SR501 - Ja-Bots
Base para sensor GP (unidad) - DynamoElectronics
How HC-SR501 PIR Sensor Works & How To Interface It With Arduino
Sensor de movimiento PIR HC-SR501 - México— ElectroCrea