A motion detector is an electronic device containing motion sensors and is integrated with or connected to other devices that alert the user of the presence of motion.

Motion sensors make an electric signal by transforming the detection of motion into it. The detection of motion can be achieved by measuring optical or acoustical alterations in the field of view.

Usually motion detector is connected to a burglar alarm used to alert the home owner or monitoring service after it detects motion.

A motion detector equipped with a timing device is called an occupancy sensor. It senses when motion has stopped for a specific time and gives a light extinguishing signal. This kind of device prevents illumination of unoccupied spaces, for example, public toilets.

The Motion Detector uses ultrasound to measure distance. This detector emits ultrasonic pulses that are reflected from an object, and then detected by the device. The time it takes for the reflected pulses to return is used to calculate position, velocity, and acceleration. This allows you to study the motion of objects such as a person walking, a ball in free fall, or a cart on a ramp.

Sensors

These are the three types of sensors that are used in motion detectors nowadays.

• Ultrasonic. It sends out emitting ultrasonic impulses and measures the reflection of a moving object.

• Microwave. Microwaves are bounced off an object. This sensor’s functions are similar to those of a police radar gun.

• Passive infrared sensors. They detect the alterations in the infrared spectrum and look for body heat.

Passive Infrared Sensors (PIR)

Passive Infrared Sensors are electronic devices that measure infrared radiation in the field of view. They are often used in PIR-based motion detectors. When an infrared emitting source with one temperature passes in front of a source with another temperature, it detects motion. The infrared radiation, which is emitted by all objects, is invisible but can be detected with the help of special electronic devices.

Such sensors are called passive because they don’t emit any kind of radiation, they just accept it.