Editing Security alarm (section)

===Electro-mechanical (shaker) sensors===
These [[Electromechanics|electro-mechanical]] devices are mounted on barriers and are used primarily to detect an attack on the structure itself. The technology relies on an unstable mechanical configuration that forms part of the electrical circuit. When movement or vibration occurs, the unstable portion of the circuit moves and breaks the current flow, which produces an alarm.  The medium transmitting the vibration must be correctly selected for the specific sensor as they are best suited to different types of structures and configurations. These systems are low cost and easily installed on existing fences, but can only be fence mounted and are unable to analyze differences in the pattern of vibrations (for example, the difference between gusts of wind and a person climbing the fence). For this reason, this technology is gradually being replaced by digital [[accelerometer]]-based systems.