Ultrasonic Sensors

Ultrasonic sensors use frequencies around 30khz. These sounds are inaudible for humans yet many dogs can hear them and may find them annoying. The transmitter bounces waves off of walls, furniture, windows and ceilings and when the room has stabilized, the alarm is armed.

There are limitations that affect their use in home security settings. Jingling keys and ringing telephones may set off the alarms. Since ultrasonic sensors don't detect very fast or slow moving objects, an intruder could hide behind an object and move across the sensor's viewable area and not set off. Although this problem has been dealt with in some models, ultrasonic sensors are not the best choice for home security systems.

The disadvantage of ultrasonic sensors is that they don't work well in rooms with wall to wall carpeting and drapery. The sound waves from the transmitter get absorbed by these materials and are too weak to return to the sensor.

Infrared Sensors
Acoustic Sensors
Vibration Sensors
Photoelectric Sensors

Learn more about home security systems.