Wireless motion sensors

Wireless infrared (IR) motion sensors that do not require wiring are one of the most popular devices for providing automated control of the security of a room or any other territory. This can be the territory of a dwelling, a personal plot, a car parking, an industrial facility or an office building. Such a sensor is a miniature device, the function of which is to detect a moving object in its area of ​​operation and turn on the alarm.

Wireless communication between the sensor and the alarm unit is via a secure radio channel, and the transmission frequency is usually 433 MHz, but it may also differ, for example, there are sensors that transmit an alarm at a frequency of 868 MHz.

The distance between the alarm unit and the wireless sensor should not exceed 100-200 meters, subject to direct visibility. Obstacles significantly reduce the interaction distance. If the distance is still too long, you can purchase a wireless signal amplifier.

The alarm unit and the IR sensor must first be connected by setting the code of the alarm unit with jumpers (jumpers) to the sensor, then it will be able to work with the specific alarm unit whose code is set. There are sensors with a training code, then you do not need to rearrange any jumpers, you just need to simultaneously press the buttons on the sensor and on the alarm unit.

The alarm unit, in turn, is equipped with a GSM module with a SIM card, due to which the alarm signal received from the sensor will be transmitted in the form of an SMS message to a given cell phone.

Most common wireless passive infrared motion sensor equipped with a special temperature detector located inside the device. The detector responds to infrared (thermal) radiation emitted by the human body, and thus registers the movement of a person in his working area.

The design of the sensor is such that when the heat source moves in the zone of its action, a configuration change occurs, focused by a special lens on the detector, received from the body of infrared rays, it is from this change in the configuration of the rays that the object's motion is determined. The most common passive infrared motion sensors have a working area with a radius of up to 15 meters with a view of up to 110 degrees, so it is advisable to use them in the rooms where they are installed, traditionally, on the ceiling in the corner.

Some sensors of this type have settings to prevent triggering of the movement of pets.

A kind of passive infrared sensor is sensor type "curtain", which has a limited detection zone in the form of a narrow beam, in shape resembling a curtain or partition. The use of such a sensor is advisable where it is necessary to stop the entry into the room through a door or window.

Another option for a passive sensor is ceiling motion sensor with a viewing angle of 360 degrees, which covers an area with a diameter of up to 10 meters underneath. This sensor, like other wireless sensors, is powered by an alkaline battery, usually of the Krona type.

For use in open areas, on the street, special types of passive sensors are used, provided with special tightness and equipped with additional protection elements from various weather factors that could damage the device.

Active infrared sensors are another form of wireless security. An active beam infrared detector consists of two units: a transmitter and a receiver.

The receiver receives infrared radiation from the transmitter, and generates an alarm when the beam crosses a foreign object. Such a system allows providing a “barrier” of up to 200 meters in length indoors and up to 100 meters in the street. The number of rays can reach ten, although usually there are one or two. Power is supplied from the network through the power supply, or from the battery. Communication with the alarm unit is also implemented via a secure radio channel. Such infrared wireless detectors are also called IR barriers.

Radio wave motion detectors - Another type of active wireless motion sensors. They are also designed to detect and record movement in a protected area. Such a detector comprises a radio frequency module consisting of a radiator and a receiver of high-frequency oscillations. Unlike passive infrared sensors, radio wave detectors emit microwave oscillations into the surrounding space.

The principle of operation of the radio wave sensor is based on the interference of radio waves of the centimeter range or the Doppler effect, when the frequency of the received signal changes when reflected from a moving object.

By their characteristics, radio wave detectors are similar to passive IR detectors and are very similar in appearance, however, they have lower noise immunity and a high level of microwave radiation. Therefore, quite often, instruments are used, which include two detectors - passive IR and radio wave.

Often, the RF module in such a device is turned on only when the IR detector detects movement in the working area, an additional check and confirmation of the presence of an extraneous object in the working area takes place. This allows you to provide a fairly high level of noise immunity of the device and reduce the level of microwave radiation, since the radio wave detector is turned on only for a short time.

Radio wave detectors can operate at one of several operating frequencies, which are set manually using a switch on the device board. This allows you to simultaneously use several sensors of the same type, operating at different frequencies, in the same room.