How do you wire an RJ45 socket in mode '3'?

Question

it has something to do with alarm systems being able to call out?

Answer 1

not sure what "mode 3" is...

for whatever reason alarm jacks use RJ45 instead of RJ12

blue white, should be connected to the dial tone, those are the center 2 pins, and may be connected to your red/green wiring...

alarm systems are usually wired as following, from the NID a wire is run directly to the alarm system, the outside wire is connected to the green/red pair, the inside wire is connected to the yellow/black pair.

at the alarm box, the green red bring the dial tone to the alarm system before it goes to any of the inside wiring, and the yellow/black brings the dial tone back to the NID to the inside wiring. it is wired this way so that even if the phone is being used the alarm can "seize" the line, disconnect the line, and dial out..