Ultra Sonic Motion Sensors

Ultrasonic motion sensors are very similar to passive infrared sensors in their overall performance. The difference is mainly the sensitivity level. These sensors operate at frequencies way above human sensitivity at about 25, 30, and 40 KHz. They are so sensitive to movement that they must be carefully calibrated. Sensors like this will react to non occupant movements like soft breezes from open windows. They provide greater coverage over the passive infrared sensors acting as radar. These sensors don’t send out sound waves, instead sending out microwave radio waves, and no I'm not talking about that thing in your kitchen.

The sensors are activated by crystal quartz that emits ultrasonic waves throughout space and air. The unit then senses the frequency of the reflected waves. So basically if an intruder were to show motion in the radar, the reflected wave’s frequency would shift causing the alarm to sound. In other words it the Doppler Effect.

You should consult a professional before you come up with the location to set up this sensor. Again, it’s very sensitive to air movements, so next to air conditioners, windows, or any place strong winds might roam are out. Installations are limited because the ultrasonic beams are easily blocked by thin materials like paper too. You may buy kits and install them yourself, but please consult a pro first. Ultrasonic sensors are more expensive and require more attention than most other sensors. Be sure it’s the right investment towards your home security needs before you buy.