General, Physical security

Motion Detection

Motion detection is a process of confirming a change in position of an object relative to its surroundings or the change in the surroundings relative to an object. Motion detection is usually a software-based monitoring algorithm which, when it detects motions will signal the surveillance camera to begin capturing the event.

An advanced motion detection surveillance system can analyze the type of motion to see if it warrants an alarm. Motion can be detected by: sound, opacity, geomagnetism, reflection of transmitted energy, electromagnetic induction and vibration. Radar intrusion sensors have the lowest rate of false alarms.

Electronic Detection

The principal methods by which motion can be electronically identified are optical detection and acoustical detection.

Optical Detection

> Infrared light

> Laser technology

A simple algorithm for motion detection by a fixed camera compares the current image with a reference image and simply counts the number of different pixels. Since images will naturally differ due to factors such as varying lighting, camera flicker, and CCD dark currents, pre-processing is useful to reduce the number of false positive alarms.

Motion sensor is a device for motion detection. It is a device that contains a physical mechanism or electronic sensor that quantifies motion that can be either integrated with or connected to other devices that alert the user of the presence of a moving object within the field of view.

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 changes in the field of view. Most motion detectors can detect up to 15 – 25 meters.

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. Such a detector may also trigger a red light camera.

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.

Types of sensors

Passive infrared sensors (Passive)
Looks for body heat.

Ultrasonic (active)
Sends out pulses of ultrasonic waves and measures the reflection off a moving object.

Microwave (active)
Sensor sends out microwave pulses and measures the reflection off a moving object.

Tomographic Detector (active)
Senses disturbances to radio waves as they travel through an area surrounded by mesh network nodes.

Please read wiki‘s articles on motion detection and motion detectors-sensors.