Abstract: Four magnetically actuable reed switches are configured in a unique biasing configuration and physical arrangement for providing a defeat resistant interlock/monitoring system with minimal switching circuitry. The switches are physically arranged so that two switches, mechanically biased in a normally closed state, lie between two switches, mechanically biased closed but magnetically biased in an open state, and are mutually perpendicular. The relative positions and orientations of the biased and nonbiased switches require two separate magnetic fields to activate the system. The system is only activated by an actuator which emits the magnetic fields required to actuate only the magnetically biased switches. The actuator magnet fields are oriented in the same direction as the biasing magnet fields. Adjustability of biasing magnets and a minimal number of switches and actuation magnets increase reliability of the system despite variations in actuator position.