Abstract: A fail-safe circuit for preventing an inadvertent communication of a signal from an input terminal to an output terminal includes a series switching network electrically connected between the input terminal and the output terminal. The series switching network contains two switching circuits electrically connected in series. One switching circuit is an electrical switching circuit and the other is an electromechanical switching circuit. The switching circuits are chosen such that defects causing the electrical switching circuit to short circuit do not affect the electromechanical switching circuit and defects causing the electromechanical switching circuit to short circuit do not affect the electrical switching circuit. The fail-safe circuit also includes circuitry for preventing inadvertent communication of the signal from the input terminal through the series switching network to the output terminal when one of the switching circuits is in a short circuited state or condition.