Yeehaaae dowgey!

if you lot are going to help out these amatuers then don't knock that fact they are rough as old boots

Please explain, Are you saying it is not a good idea to use a unused pair of the cat5 for the alarm?

Putting in another cable was not possible without ripping up a concrete street. My understand from using Cat 5 for a very long time is the pairs dont talk to one another, I thought that was the idea.

If you pass current through a wire it Will create an electromagnetic field. if you place a wire in an EMF it will induce a current onto that conductor. the more wire in the EMF the more current inducted. tis called cross talk. not good practice, ok as a temp, but as a permanent fix no good imo

Rs485 comms would normally be able to filter out this noise, but it will make it more prone to data errors

It's irrelevant - he's switching voltages. What does the speech dialler needs to be triggered (I have no idea because we run a proper company) - if you are a applying or removing 12v or 0V then run a round link through a relay which is triggered from the remote panel.

Is it not normal to remove the voltage in activation?

Therefore there is an EMF all the time the systems are clear