IR Break Beam Sensor - 

SEN0503 is an IR break beam sensor. This infrared break-beam sensor is a simple way to detect motion. This IR break beam sensor works up to 50cm with a fast and stable response of ＜2ms. With a small size of 20 x 10 x 9mm, the module can be conveniently installed in a narrow space. Besides, it can operate within a temperature of -25°C to 60°C. Power the sensor by a voltage of DC 3.0 to 5V. It can be used with Arduino for some simple motion detection, speed detection, timing, etc. in smart robot competitions. This works by having an emitter side that sends out a beam of human-invisible IR light, then a receiver across the way which is sensitive to that same light. When something passes between the two, and it’s not transparent to IR, then the“beam is broken“and the receiver will output a signal to let you know. Application includes simple motion detection, speed detection, timing.