Which jack is used to disconnect the alarm from the phone line to test line quality?

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

Answer: (C)

You’re looking at isolating the alarm’s dialing from the home phone line so you can test line quality without other devices in the line interfering. The dedicated interface for this in many residential alarm setups is the RJ31X jack. It sits between the alarm panel and the incoming telephone line and lets you disconnect the alarm’s line from the house line for a clean line test. This way you can verify dial tone and line performance while the rest of the home phones aren’t affecting the measurement, and the alarm can still dial out when needed. The standard RJ11 is just a regular phone jack, RJ45 is for Ethernet, and a modem is a device, not the test isolation point.