Ultrasonic technology is sensitive to motion toward and away from the detector; the passive infrared technology (PIR) is sensitive to motion across the field of view. Both technologies must trip in tandem to signal an alarm. Sensors should be mounted where people are most likely to cross the beam pattern and should be situated for the desired visibility or invisibility. Room size should also be factored in; too much sensor coverage will increase false alarms. PIR/microwave sensors such as Arrowhead Technologies' DL260 usually cover a larger zone than do PIR/ultrasonic sensors. For additional protection, the 5770 Shatterbox II Acoustic/Vibration Glassbreak Detector trips at the sound of breaking glass. 1 figure, 1 chart, and photographs.