Editing Security alarm (section)

===Motion sensors===
Motion sensors are devices that use various forms of technology to detect movement. The technology typically found in motion sensors to trigger an alarm includes infrared, ultrasonic, vibration and contact. Dual technology sensors combine two or more forms of detection in order to reduce false alarms as each method has its advantages and disadvantages. Traditionally motion sensors are an integral part of a home security system. These devices are typically installed to cover a large area as they commonly cover up to {{convert|40|ft|abbr=on}}, with a 135° field of vision.

A type of motion sensor was used by the Japanese since ancient times.  In the past, "(m)any people in Japan kept singing crickets and used them like watch dogs."<ref>Mathiews, Franklin K. "The Boy Scouts Book of Outdoor Hobbies," D, Appleton-Century Company, Incorporated, New York 1938, page 193.</ref>  Although a dog would bark when it senses an intruder, a cricket stops singing when approached by an intruder. The crickets are kept in decorative cages resembling bird cages, and these cages are placed in contact with the floor.  During the day, the house is busy with normal daytime tasks.  When activity reduces at night, the crickets start singing.  If someone comes into the house at night, the floor starts to vibrate.  "The vibration frightens the crickets and they stop singing.  Then everyone wakes up --- from the silence.<ref>Mathiews, Franklin K. "The Boy Scouts Book of Outdoor Hobbies," D, Appleton-Century Company, Incorporated, New York 1938, page 194.</ref>  The family is used to hearing crickets at night and knows something is wrong if the crickets aren't singing.  A similar observation was made in England about millers who lived in their mills.  A mill wheel makes a great deal of noise, but the miller only awakens when the mill wheel stops turning.