Indoor Alarm Sensors

An alarm is transmitted when a sensor activates. Activation is in response to the detection of a phenomenon such as movement, touching, temperature, and sound. Some sensors are designed for indoor use; some for outdoor use; and some can be used indoors and outdoors. Following are brief descriptions of some indoor sensors.

The passive infrared detector (PIR) is one of the most common detectors found in household and small business environments because it offers affordable and reliable functionality. The term passive means the detector is able to function without the need to generate and radiate its own energy. PIRs are able to distinguish if an infrared-emitting object is present by first learning the ambient temperature of the monitored space and then detecting a change in the temperature caused by the presence of an object.

Ultrasonic detectors transmit sound waves that are inaudible to humans. The sensor activates when it detects a change in frequency due to object motion. This is caused when a moving object changes the frequency of sound waves around it

Photoelectric beam systems detect the presence of an intruder by transmitting visible or infrared light beams across the surface of an area. When a beam is interrupted, such as when an intruder walks into a room, the sensor activates. To improve detection, beams are often employed in stacks of two or more.

The glass break detector is used for internal perimeter building protection. When glass breaks it generates sound in a wide band of frequencies. Glass break acoustic detectors are mounted in close proximity to the glass panes and listen for sound frequencies associated with glass breaking.

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