The Siemens 3RH1921-1KA11 is a front-mounted auxiliary switch block from the SIRIUS series, designed to expand the functionality of 3RT1 contactors and 3RH1 contactor relays of size S00. This component provides additional signaling contacts for control and interlocking circuits. It features one normally open (NO) and one normally closed (NC) contact, offering flexibility for various industrial automation and control applications. The unit is easily snapped onto the front of the contactor, and its screw terminals ensure a reliable and secure electrical connection. This auxiliary switch is essential for monitoring the switching state of the main device and implementing safety-related functions.