A motion sensor is a device that is used to detect the presence of movement in a particular area. A PIR Motion sensor is usually used for security purposes.
Active motion sensors use a battery to power their internal electronics and they detect motion by emitting pulses of infrared light or ultrasound waves towards their surroundings.
Ultrasonic motion sensors emit high-frequency sound waves (ultrasound) which bounce off an object and then return to the sensor to measure the time it took for the sound wave to travel from one point to another.
