A person or vehicle will always have a temperature contrast in respect to the background, producing a change of radiation within the field of view when passing through it. This temperature contrast can be as little as 1°C (either positive or negative) for a person at the nominal distance of 50 feet (15m) to trigger the alarm. Each person, object or animal emits infrared energy as a function of its surface temperature and size. The PIR technology, of the MS16, emits no detectable radiation and will not interfere with adjacent sensors. The microwave portion of the MS16 transmits microwave energy into the protected area. Under normal conditions (no intrusion), the receiver establishes a reference level based on signals reflected from the protected area. Motion by an intruder causes the receiver signal to change relative to the established reference threshold and an alarm is generated.