Conventional motion detectors are usually used for this purpose. A sensor responds to a person’s movement, triggering a pre-defined function – from activating a display to switching on a camera. Doors have been opening for us for years without any contact and the light switches on as soon as we enter a room. Especially in smart homes, the possible use cases are increasing considerably. Multimedia systems or even kitchen appliances switch from standby to active operation or communicate with us as soon as they are informed of movements. In conjunction with a higher-level control system, not only can small areas and individual appliances be automated, but functions throughout the entire house. For example, through the motion detection, the heating and air-conditioning systems and roller shutters can be adjusted without any active intervention by people. Automation is a contactless interaction option that makes our everyday life more convenient, efficient, and sometimes even safer.

A related example application for passive control with radar technology are conventional alarm systems. Because motion detectors are also in use here. The devices are meant to remain unnoticed by potential criminals, so that they trigger them unwittingly through their movement. To this end, the sensors continuously send pulses to detect persons creeping up immediately and to detect them before they take action – even in the dark. Passively, moving objects or people activate security applications such as signalling, lighting, and camera systems and set off an audible alarm or cause a video camera to start recording, for example.

Depending on the requirements of the intended use, the functional equipment of the systems can be simpler or more extensive. This provides the user with individual customisation options, which help to improve performance. The aim is to sound an alarm only in the event of security-relevant movements: for example, for a creeping burglar, but not a roaming dog or a passing car.

Another form of passive activation of technical functions can be found, for example, in industrial applications. Here, the possible use cases are very diverse. In warehouse and production facilities, gates, barriers, turnstiles, and doors automatically open for arriving vehicles or approaching people. Escalators and conveyor belts also start by themselves if they detect a movement or a person’s presence without anyone pressing an on button. Applications that boast not only greater convenience but also better safety are more complex, but all the more important. Sensors protect us from dangers by detecting the presence or movement of persons and objects in the surroundings. For example, if we inattentively get too close to a danger zone, we unconsciously trigger a safety measure (e.g. machine stop, speed adjustment, block-off, or alarm signal). This way, the technology protects us from collisions, injuries, or material damage. Passive interaction with radar sensors is becoming increasingly important for us, as occupational safety requirements are also becoming more stringent.