Changing Your Phone Service

IMPORTANT: Changing (or repairing) your phone wiring can result in your alarm system failing to communicate with the monitoring service.

ProTech Warning: Wiring technicians often do not understand how your alarm system's RJ31X jack works to seize your phone line in an emergency.

Why is this important?

The information below will help you understand the important issues so that you can advocate for a proper installation. You may want to share this with your technician before he/she begins work.

ProTech Inc. installations have a RJ-31X jack. This is usually an ivory colored plastic box with an 8-pin modular (Ethernet style) phone plug located by the main alarm system panel (metal box.) This jack has two functions:

  1. Phone line seizure: The jack routes the phone signal into the alarm system first, then distributes it to the phones in the house, which allows the alarm panel to provide "line seizure." Line seizure prevents a burglar from taking a phone off the hook to interrupt communication by the alarm system.
  2. Troubleshooting phone problems: The RJ-31X jack also allows you to unplug the alarm system as if it were just another extension phone, which eliminates the alarm system as the cause of a phone trouble condition.

How the RJ31X connection works: The phone line from the street enters the phone distribution point (typically a gray service box on the side of your house) and then travels on a pair of wires to the RJ-31X jack. The line leaves the jack on a separate pair of wires in the same cable and returns to the phone distribution point, where it connects to the extension phones in your house. When the alarm system is plugged into the RJ-31X jack, phone signals go through the alarm system and back into the jack before they continue their route to your extension phones. When the alarm system is unplugged from the jack, an internal switch in the jack routes the phone signal directly back to the phone distribution point, bypassing the alarm system.

For Comcast Customers: According to Comcast's HOME SAFE HOME brochure: ( "Comcast Digital Voice DOES support most modern home alarm systems today. Some companies offering Voice over Internet Protocol [VOIP] today use the public Internet and self-installation services, which could result in issues with your home alarm system. Because Comcast uses its own managed network, not the public Internet, we can ensure the quality of service required to support most modern home security systems. In addition, we have professional installers who are trained to install our service so that it does not impact your home alarm system. . . At your request, Comcast will install a hard-wired, dedicated feed between your Comcast eMTA (Comcast-supplied enhanced Multimedia Terminal Adapter) and your monitored alarm panel..."

When Comcast installs Digital Voice, they often connect their Internet and telephony modem equipment (EMTA) near your computer and plug it into the nearest phone jack. The result is that your RJ31X jack no longer receives a phone signal from the phone distribution point (where AT&T connected its phone line from the street.) The incoming phone signal is now connected like another phone extension. Because the RJ31X is connected backwards, when it tries to communicate to the monitoring station the alarm system actually disconnects itself (as it tries to cut-off the extension phones and seize the phone line.) When the system goes into alarm it can't communicate to the monitoring station.

Technicians may try to fix the alarm communication problem by connecting their phone signal to the incoming terminals of the RJ-31X jack, using your existing phone wiring. Line seizure will not work connected this way. In other words, if a technician connects a line into the alarm system as if it were just another phone, the alarm system won't be able to communicate when a burglar takes an extension off the hook.

So, what is the correct solution? The first phone signal out of the Comcast EMTA (or for an AT&T technician- the phone distribution point) must be wired directly into the alarm's RJ31X jack in one of two ways for it to work correctly:

  1. Comcast needs to provide their phone signal from the Comcast EMTA at the same point that your previous company supplied their signal. This is usually a grey service box on the side of your house. This will make it easier to perform service or to change back to AT&T if you decide to do so in the future.
  2. Install a hard-wired, dedicated feed between your Comcast eMTA and your monitored alarm panel. Comcast should do this at no extra cost. The phone signal must connect to the incoming terminals of the RJ-31X jack.

Always test your alarm system monitoring after any phone service and before the technician leaves your house.