Motion sensor selection

Types of motion sensors

According to the principle of operation , the detectors distinguish:

• Infrared. These scanners use a pyroelectric sensor that scans the IR radiation in the place where it is located. Usually, an infrared type motion detector consists of two devices: the first generates radiation, and the second receives it. When there is an object with a different temperature between the devices, the sensor signals penetration. Infrared devices are often used to protect the perimeter.
• Ultrasonic. They generate radio waves, which, reflecting from the object, return to the device and determine the distance to it. If, after scanning, the device determines that the distance to the object has decreased or increased, then it will give a signal. Ultrasonic scanners cannot be used in rooms with animals (constant triggering, as well as harm to the animals themselves, which are sensitive to a frequency of 30 — 40 kHz) and with transparent walls, since they can falsely detect the movement of an object in an adjacent room.
• Microwave. The principle of operation is similar to ultrasound: the device generates waves, in violation of which the detector is triggered.
• Combined. These devices combine infrared and microwave or infrared and ultrasonic principles of operation. Such models are able to simultaneously detect the movement of an object, as well as react to glass breaking. Combined devices are more expensive, but they are able to provide more accurate information about the condition of the room in which they are installed.

The purpose of motion sensors can be as follows:

Glass break alarm

• The crash detector. These detectors react only to glass breaking. They can be contact and contactless. The first ones are attached directly to the glass and, if it is damaged, they sound a signal (siren). The latter can be installed at some distance from the window, and they react to the slightest fluctuation of the glasses (strong wind does not count).
• Security guards. This type of device is used for embedding in an alarm system. They work from a voltage of 12 or 24 V.Security devices are installed so that their range covers the area where penetration is possible, for example, doors and windows. They are used to detect unwanted persons in supermarkets, warehouses, banks, offices, as well as in apartments and cottages. Some security devices may additionally have breakage sensors and react to damage to the glass of door and window openings. Security motion sensors can be both infrared and ultrasonic.

Lighting Detector

• Light sensor. The vast majority of these devices are infrared and are designed only to turn on/off street or indoor lighting. When a person appears in the range of the unit, the sensor is triggered and turns on the lighting. Due to their highly specialized purpose, they are the cheapest and easiest to use.

What should you pay attention to when choosing a sensor?

Before purchasing a detector, pay attention to the following parameters and possible additional functions:

• Immunity to animals. This function protects the unit from false triggering if there is an animal in the house. In different models, different response parameters are set relative to the pet's weight from 10 to 20 kg. This feature is especially convenient for commercial purposes when there is a watchdog in a protected area.
• Wireless connection. Wireless units look much more aesthetically pleasing without a bunch of wires, and they are not as noticeable as wired ones, so it will not work for an attacker to turn them off just like that. However, the devices run on battery power, so you should always check the charge so that they do not turn off at the most inopportune moment.
• Adjustment of illumination and response time. These functions are relevant only for lighting sensors. Such models can be adjusted according to the degree of illumination: in the daytime it is inactive, and as soon as it gets dark, it turns on. It is also possible to set the sensor response time between its activation and deactivation after the human movement stops. This is very useful for entrances where the light should not be turned on/off too often to avoid equipment wear.
• The angles of the scanning area. Each device has horizontal and vertical scanning angles of the room. They determine which area a particular device will cover. Vertical wall panels cover almost the entire space (a feature of installation), but not horizontally. Therefore, if you have several entrances or windows in the room, then take it with a large viewing angle. Both indicators are important for ceiling ones, so “full visibility” will be provided by models with 360-degree viewing angles.
• Scanning range. This parameter affects the distance at which the device is able to scan the movement of the object. Security units are capable of “finishing off” at a distance of 10 — 15 metres, while powerful IR barriers have a scanning range of up to 250 m.
• The temperature of normal functioning. This parameter is important when choosing a street model that should work all year round. For most regions of the CIS countries, devices with an operating temperature of up to -40 °C are suitable. For colder ones, you should choose individually.