Motion detectors are end devices that monitor the presence of a person in the vicinity and then issue some type of notification. The notification can be a sound, light, or transmission of a message to another unit such as a control panel, alarm system, or cloud application. Such motion detectors are widely deployed in households, commercial buildings, and other facilities. The detectors can be installed indoors or outdoors and are used mainly as intrusion-detection systems. In recent years, motion detectors have been deployed in other applications such as automatic doors, automatic lights, airflow control of heating and cooling systems and various other functions. Wireless motion detectors use the wireless medium and transmit their detection status to other units so that further action can be taken. For example, they can transmit their status to a control panel to activate an alarm if the security system is armed.
Common-motion sensing technologies are passive infrared (PIR), ultrasonic emitters, and microwave emitters, described as follows.
- PIR – Senses changes in IR radiation within the field of view determined by the Fresnel lens. PIR is sensitive to anything which generates heat or changes in temperature.
- Ultrasonic emitters – Output signal is a measure of the Doppler Effect produced by the transmitted signal being reflected and received from a moving target (Doppler radar).
- Microwave emitters – Operation is similar to the ultrasonic sensor except for the carrier frequency (40 kHz to 100 kHz for ultrasonic versus 10 GHz or 24 GHz for microwave).
Each motion-sensing technology has advantages and disadvantages in terms of miss detection versus false alarm trade-off, due to different sensitivity levels in various environments. Some solutions use more than one method for better reliability.
In the future, smarter motion detectors will detect not only motion but also the type of the motion (see TIDA-01069 as a reference for such a solution). These smart solutions are designed to distinguish between the movements of either an adult person, child, pet, and flames in a fireplace, or even a person falling. The detectors analyze the different signature that each type of movement creates.
The smarter the motion detector is, the more it requires connectivity and cloud connectivity. If the detector can detect different situations, then it can react and provide the correct action needed, which can require different communication methods. For example, when a senior citizen's fall is detected, the system must communicate with emergency services through the cloud. When an adult's movement is detected, the detector communicates to the security company and to a siren device. When a small child is detected unexpectedly, the system must initiate a message on the phone of the owner.
Whether it is PIR, ultrasonic, or microwave emitter technology, a traditional motion detector or a smarter one, the challenges are similar when it comes to the communication architecture of the system as well as the MCU and low-power requirements.
In many cases, wireless motion detector systems are part of a wider security system in which they function as data points for intrusion detection, along with door and window sensors or glass-break detectors that monitor the status of entry points. In such systems, the motion detectors are usually connected to the main security panel. In other cases, motion detector systems are smaller systems that contain one or more sensing units, an alarm unit, and in many cases a panic button that arms the system. These systems are targeted for DIY users and provide complementary solutions to other security measures. In both cases, wireless systems are the preferred and desired solution, because they avoid the problems presented by wires and reduce installation and maintenance costs.