Throughout history, humans have sought to protect their life, property and possessions. In early societies, guards, watchdogs, traps and even noisemakers provided security. Fire was used to baffle wild animals and keep them at bay. In fact, in the opening scenes of the movie, Raiders of the Lost Ark, you see a security system devised to apprehend its violators: When Indiana Jones tripped the mechanism, he was pursued by a huge, rolling boulder. As centuries passed and human accomplishments became more noteworthy, some rather engaging and sophisticated devices were developed to insure man's security. But until the discovery and harnessing of electricity, no device or protection scheme could be expected to provide any real degree of assurance or consistent peace of mind.

Classifying alarm systems In terms of electrical alarms, the vast majority of security systems fall into three broad designs: local alarm, monitored systems and silent alarm.