Which interface isolates the alarm from the telephone line for testing line integrity?

• A. RJ31X jack
• B. RJ11 jack
• C. RJ45 jack
• D. Modem

Answer: (A)

The idea being tested is how the alarm can isolate and test the telephone line so it can verify line integrity without other devices on the same line getting in the way. The interface that provides this protection is the RJ31X jack. It sits between the building’s incoming phone service and the alarm panel (and any house phones). When the panel needs to dial or run a line test, it seizes the line through this jack, creating a dedicated path for the alarm’s communication and ensuring the test isn’t affected by other devices on the line. Normal phone use can continue when the system isn’t dialing, but during testing the alarm has a clean, isolated connection. The other options aren’t designed for this purpose: a standard RJ11 is just a basic phone jack, RJ45 is for Ethernet, and a modem is a device, not the isolation interface used for line integrity testing.