Alarm Components

Circuit Break

• Electric alarm systems have a break in the circuit that sounds the alarm. A trigger closes a switch so the circuit is completed. Electricity can then flow through the alarm circuit to sound the alarm’s siren.

Siren

• The siren itself sounds out when its circuit is closed. In older systems, a bell rang to sound the alarm, but now such alarms are hard to find. With the electrification of alarms, bells have given way to speakers. They can be quite loud. Personal alarms go up to 130 decibels, which is 10 times the human pain threshold.

Transmitter

• Some home and car alarms, in addition to the siren, also transmit alerts. These transmissions are not just to the police but also to a pager or your computer. This helps with car alarms that may be parked too far away for the owner to hear. It helps with home alarms when you are away, especially if your security package includes home cameras that you can view online.

Power Source

• A burglar alarm’s power source must not be easily severable. If the alarm system transmits a signal the police, it must do so quickly, before a burglar cuts its power. It must also allow enough time for the owner to turn it off upon returning home.

Interface

• The owner must have an interface through which to arm and disarm the alarm. In the case of a burglar alarm, the interface can’t be easily overridden by the burglar. Therefore, a code is necessary. Some alarm interfaces include panic buttons to the police and medical respondents, since home invasions can occur after the owner has turned the alarm off and medical emergencies don’t trigger mechanical alarms.

Motion Sensor

• Car alarms and some home alarms use motion detectors. In car alarms, the trigger movement is the car’s shaking (from a window being broken, e.g.), while in homes the trigger movement intercepts a light beam or causes some other sudden light change the sensor can detect. A tow truck’s elevating one end of a car can usually deactivate the motion sensor. Presumably towers are not thieves and the alarm has gone off long enough to alert the owner.