Abstract: A current sensor provides a positive voltage when a non-desired condition is present, such as rotation of machinery above a predetermined speed, and a gating circuit causes contacts of a relay to close whenever the rotational speed drops below such predetermined speed, that is when the desired condition is achieved. The gating circuit also closes these relay contacts in response to failure of the electrical power to such gating circuit. The circuit includes a P-N-P transistor in series with the relay coil, which transistor is switched on or off by a NAND gate. A low level signal to the base of the P-N-P transistor is provided through the NAND gate when the inputs to the gate are high, thereby providing a fail-safe feature for the relay because one of the NAND gate inputs is provided from the sensor's reference voltage through a Schmitt-trigger circuit.