Editing Security alarm (section)

===Microphonic systems===
[[File:Strain -sensor cable installation.jpg|thumb|Strain-sensor cable installed on a chain-link/barbed-wire fence]]
Microphonic systems vary in design (for example, [[Time-domain reflectometer|time-domain reflectrometer]] or [[Piezoelectric sensor|piezo-electric]]) but each is generally based on the detection of an intruder attempting to cut or climb over a fence. Usually the microphonic detection systems are installed as sensor cables attached to rigid chain-wire fences, however, some specialized versions of these systems can also be installed buried underground. Depending on the type, it can be sensitive to different frequencies or levels of noise or vibration. The system is based on coaxial or electro-magnetic sensor cable with the controller having the ability to differentiate between signals from the cable or chain-wire being cut, an intruder climbing the fence, or bad weather conditions.

The systems are designed to detect and analyze incoming electronic signals received from the sensor cable, and then to generate alarms from signals which exceed pre-set conditions. The systems have adjustable electronics to permit installers to change the sensitivity of the alarm detectors to the suit specific environmental conditions. The tuning of the system is usually done during commissioning of the detection devices.

Microphonic systems are relatively inexpensive compared to other systems and easy to install, but older systems may have a high rate of false alarms caused by wind and other distances. Some newer systems use [[digital signal processing|DSP]] to process the signal and reduce false alarms.