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Alarm System Communications
Most residential and commercial alarm systems use "digital communicators" to transmit the alarm signal to the alarm monitoring central station. While very cost effective, digital communicators have one weakness: they depend on the telephone line to transmit their message. If the telephone line is cut or otherwise disabled, the alarm system cannot transmit its signal.
Many criminals are aware of this weakness and will cut the telephone line prior to committing a burglary or other crime. If the alarm system is totally dependent on telephone lines, the system is rendered useless if the telephone lines are cut. In most cases, neither the facility owner nor the central station is aware that the telephone lines have been disabled until after the crime has been committed.
There are several options that the facility owner should consider to overcome the weakness of telephone lines:
Protect the Telephone Line Where It Enters Your Building
In many cases, telephone cables are installed overhead between the telephone pole and your building. Most of the time, exposed telephone cable will be routed down the side of the building and will terminate at a little box (called a "protector") which is installed two or three feet above the ground. If your telephone cables are installed this way, they are easily accessible to an intruder. Two suggestions:
Protect the telephone cabling on the outside of the building by installing it in metal conduit.
If possible, try to have the protector installed on the inside rather than the outside of the building. If this is not possible, install the protector in a locking metal enclosure and provide a tamper switch that activates the alarm in the event that the enclosure is tampered with.
(Review local telephone company requirements before making any changes.)
Install a Telephone Line Monitor
Most alarm systems can be equipped with a device known as a "telephone line monitor". This device constantly watches the telephone line and can detect when the telephone line has been cut. The telephone line monitor can sound a buzzer on the premises to alert the facility owner when there is a problem with the phone line. The telephone line monitor can also be wired to sound an audible alarm (such as an outside siren) when the telephone line has been cut.
Most telephone line monitors use a simple electronic circuit to detect the presence of the telephone line and are not perfect. In some cases, the telephone line may be defective but the telephone line monitor will think it is OK. Telephone line monitors will also occasionally report that the telephone line is defective at times when it working fine.
Install a "Line Supervision" System
Many alarm companies offer a "line supervision" type of alarm transmission system. These systems either use a special type of telephone line or send out a special signal over your regular telephone line. When the telephone line is cut or disabled, the central station is immediately notified. There are several types of line supervision systems, including multiplex, derived channel, and others. Most line supervision systems require that an additional monthly fee be paid to both the alarm company and the telephone company.
Install a Back-up Alarm Communications System
For best security, install a back-up method of communicating the alarm signal to the central station. This type of system allows alarm messages to be transmitted even though the telephone lines have been cut. Three popular types of back-up communications systems are:
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