These types of wireless sensors use the infrared light spectrum which is an invisible
light that emanates from any heat source. Infrared sensors (passive infrared)
compare the heat of any object passing through the secure zone to that of the
background setting such as a wall, and/or measure the rate of change in temperature
of an object. These sensors can detect fires or malfunctioning appliances.
Infrared
sensors are cheaper than microwave sensors and ultrasonic
sensors and are generally smaller and more reliable. Since they don't respond
to sharp impacts, radio waves or vibrations they are commonly part of packaged
home security system.
Some drawbacks to infrared motion sensors is
that they don't cover a full room. The scanned area is really numerous linear
areas, much like fingers pointing into the room. The areas between the fingers
are not covered. Many systems come with a variety of lenses which allow the user
to select the type of security coverage they would like to have for their secure
zone. |
