Motion detector
From Wikipedia, the free encyclopedia
A motion detector is a device that contains a motion sensor and is either integrated with or connected to other devices that alert the user of the prescense of motion.
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[edit] General
An electronic motion detector contains a motion sensor that transforms the detection of motion into an electric signal. This can be achieved by measuring optical or acoustical changes in the field of view.
A motion detector may be connected to a burglar alarm that is used to alert the home owner or security service after it detects motion.
An occupancy sensor is a motion detector that is integrated with a timing device. It senses when motion has stopped for a specified time period in order to trigger a light extinguishing signal. These devices prevent illumination of unoccupied spaces like public toilets.
[edit] Sensors
There are basically three types of sensors used in motion detectors today.
- Passive infrared sensors (PIR)
- Detects changes in the infrared spectrum. Looks for body heat.
- Ultrasonic
- Sends out an emitting ultrasonic pulses and measures the reflection of a moving object.
- Microwave
- Microwaves are bounced off an object. Similar to a police radar gun.
[edit] Dual-technology motion detectors
Many modern motion detectors use a combination of different technologies. These dual-technology detectors benefit with each type of sensor, and false alarms are reduced. All companies have the option to use PIR/Microwave Motion Detectors that have "Pet-Immune" functions which allow the detector to ignore pets that weigh up to 40 pounds (wireless models) or 80 pounds (hard-wired models).
Often, PIR technology will be paired with another model to maximise accuracy and reduce energy usage. PIR draws less energy than microwave detection, and so many sensors are calibrated so that when the PIR sensor is tripped, it activated a microwave sensor. If the later also picks up an intruder, then the alarm is sounded.
