Abstract: In the particular embodiments described in the specification a device is provided to protect against failure of a switch connected to a load and to give an alarm that the switch has failed. The device includes a circuit in parallel with the switch which contains a transistor and a diode to cause such voltage drop in the circuit as to prevent current flowing through a second diode when the switch is closed. If the switch fails open, the potential at the load side of the switch will drop, and the second diode will allow current to flow to the load through the circuit. The current flow produces a potential difference across the first diode to turn on another transistor to cause an alarm to be given. The device may be used to test such switches without affecting the load controlled by the switch.