The RJ-31X is a special type of phone jack required to connect an alarm device to a telephone network. The RJ set shown to the left includes the interconnection cord to interface the alarm with the telephone jack.
When wired correctly for proper line seizure, it will allow an end user or service technician to easily, without tools, disconnect an alarm communicator from the telephone network without disrupting the premise wiring or alarm system's wiring.
The FCC requires this device, or similar, for any piece of equipment installed which would cause the loss of dial tone upon failure, including an alarm panel or other dialing equipment connected to the phone lines.
The jack and connection technically should be "readily available" should the need arise, without tools or prior knowledge. How this falls into location is somewhat of a gray area in terminology and definitions, as well as security. It should be "technically" installed outside of the alarm control unit, so access to the control, which may be screwed or locked shut, is not necessary. Some companies and installers prefer to install them within the alarm control, or in close proximity, but this is subject to interpretation to the definition and conventions in the area. Provided your alarm control unit is located in a secure area and not subject to tamper, there is no reason not to provide the jack and cord in an accessible manner.
The jack is not a standard telephone jack, and connecting anything other than alarm equipment will cause damage to the jack or equipment.
Wiring between the jack and the telephone network interface needs to be done using a minimum of Category 3 wiring.