Abstract: An electro mechanical liquid level sensor is disclosed. The sensor comprises a magnetically operable switch which responds to liquid level in a container to complete a circuit for actuating a warning light or the like. The switch comprises an electrical contact operative in response to a magnetic force which is movable in accordance with liquid level whereby the circuit is completed upon a predetermined change in liquid level. The movable parts of the sensor are self-aligning. The movable contact may be maintained in the circuit closed position independent of liquid level until reset.