In an alarm system, an EOLR is used to:

• A. Supervise a protective circuit
• B. Provide battery backup
• C. Indicate door status
• D. Trigger audible alert

Answer: (A)

End-of-line resistors are used to supervise the wiring of a protective circuit. They provide a known resistance at the far end of a supervised loop so the control panel can continuously verify the entire circuit is intact. If the wiring opens or shorts somewhere along the run, the resistance changes and the panel recognizes a fault or tamper condition.

This is why the resistor’s job is to monitor the circuit itself, not to provide battery power, indicate door status directly, or trigger the alarm sound. Door status is read by door/trigger sensors, and audible alerts are initiated by the panel when a fault or alarm condition is detected.