The ELMON rail 41-822 switching device is used to evaluate sensors such as safety contact mats, safety contact edges and safety bumpers for securing crush and shear locations. An ASO sensor can be connected to the switching device. The steady-state current monitoring of the sensor is made possible by an integrated terminating resistor in the sensor. Furthermore, the device can also evaluate a sensor in four-wire technology. If the desired steady-state current flows, the safety relays are driven and the switching contacts closed. If the sensor is operated or the sensor circuit is interrupted, the relay switching contacts open.