Reed switch builtDesigned to detect when a door is closed or openUse provided counter plate when stationary part is nonWhen the plate is in contact with the catch, the circuit is open. When the plate is removed from the catch, the circuit is closedSpecial design provices screw mounting options in 2 different orientations WARNING: This product can expose you to chromium, nickel, which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.P65WARNINGs.ca.gov.