Occupancy sensors are provided that do not require an external power source in order to operate. The sensors operate with a low voltage non-rechargeable battery and are fully functional for at least about 15-20 years. The sensors include a relay output capable of switching high or low voltage and high or low current with virtually no generated heat. The sensors require no warm-up period, no minimum load, and no external ground connection. The sensors are always active and are easily installed, having two electrically interchangeable outputs for coupling to, for example, a load and a load power source.