Modern alarm controls are solid-state devices, and do not use the relays that the older alarm panels used to go into alarm. They make use of relays to modulate the alarm notification device as needed. And they use a relay to seize the telephone line to communicate to the monitoring station. Most switching devices are N.C. (normally closed) circuits, so when the device is not in an alarm condition, the circuit is closed. Most alarm circuits (zones) are also set up to open or close on reading a certain resistance, usually between 1K and 5K ohms when inactive and double the value when active. This wiring system is called dual loop and allows for both alarm and anti-tamper detections to be incorporated into one circuit (anti-tamper occurs when the resistance level moves outside normal open/close values). This is the standard circuit in most modern systems.
High-security alarm controls use current and impedance monitoring on the premises, and may report to the central station via dedicated voice-grade or DC (obsolescent) circuit, or by means of multiple-drop AC grade transmitter (multiplex). Early (c.a. 1980) solid-state alarm controls used shunt switches or momentary closures on the key circuit to arm or disarm the control. Modern controls can use these arming techniques, but more frequently use a keypad which sends operating information to the control. Thus, there is no point in attacking the keypad, as there is no intelligence in the keypad, it is all located in the control. Also, many controls feature integrated transmitters, using wired telephony or optionally, cellular telephony. These controls also monitor the status of the telephone line, and can be programmed to trip if the telephone line fails (or is cut). The controls which utilize cellular telephony report either periodically or at a pseudo-random interval to the central station, and a failure to report will result in a dispatch.
High-security alarm controls use current and impedance monitoring on the premises, and may report to the central station via dedicated voice-grade or DC (obsolescent) circuit, or by means of multiple-drop AC grade transmitter (multiplex). Early (c.a. 1980) solid-state alarm controls used shunt switches or momentary closures on the key circuit to arm or disarm the control. Modern controls can use these arming techniques, but more frequently use a keypad which sends operating information to the control. Thus, there is no point in attacking the keypad, as there is no intelligence in the keypad, it is all located in the control. Also, many controls feature integrated transmitters, using wired telephony or optionally, cellular telephony. These controls also monitor the status of the telephone line, and can be programmed to trip if the telephone line fails (or is cut). The controls which utilize cellular telephony report either periodically or at a pseudo-random interval to the central station, and a failure to report will result in a dispatch.
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