In the case of reflex sensors, a fixed reflector (e.g. a small metal plate) is mounted facing the device. The switching range is set to this reflector. If an object comes between the ultrasonic sensor and the reflector, the sensor no longer recognizes the latter, which causes the output to switch. The Contrinex ultrasonic Reflex family comprises Small (M18) devices with short housings, including 90° sensing and teach-in. Use of a reflector eliminates the blind zone, so that sensing ranges extend from 0 to 700 mm.