A Mode 3 socket is used to connect an alarm system or a personal medical device to the phone line for monitoring purposes.

Installing a Mode 3 socket must be done before the first phone socket on the premises.
The correct wiring method of a Mode 3 socket, ensures that the alarm system has priority over the phone line and is able to dial out in the case of an emergency.

This is regardless whether the phone line is in use, left off the hook or if a phone has been ripped out of the socket by an intruder.

Mode 3 and ADSL Broadband

If the alarm system is sharing the same phone line as an ADSL Broadband service, then it must be filtered with a good quality ADSL Central Splitter. Failure to do so will result in internet drop outs, slow speeds and even faulty operation of the alarm system. Below is a typical alteration of wiring to facilitate a ‘Mode 3’ connection.