What are EOL resistors and why should I have them?
An End-Of-Line resistor supervises the wiring between the alarm panel and the switch. Some panels have a limited number of detection zones and do not require EOL resistors. But if the panel can use EOL resistors to supervise the wiring, the resistors should be used. If more than one detection device is on a single detection circuit, the EOL should be at the last device. When feasible, every alarm detection device should have an EOL resistor at the device. If the EOL resistor is at the burglary contact on a door, the panel sees the wire open when the door is opened and sees the resistor when the door is closed. The thief who shorts wires together hides the EOL resistor from the panel, letting the panel know that something is going on. The thief who cuts the wire causes an open circuit, the same as if he had opened the door. Hold-up alarms and Fire alarms use an “open circuit” detection scheme. The panel normally sees the EOL resistor at the end of the detection circuit. A short on the w
