Ian McDonald wrote:

If the alarm is on the phone side of the filter why can't you use ADSL elsewhere and why don't you need filters elsewhere?

Unless by phone side you mean behind the filter instead of in the phone socket of the filter which would then make sense.

All that an ADSL filter is, is a cheap bandpass filter.

In general alarms are wired directly into the telephone system, not to a plug which goes into a socket. If it was, then eveyrone would just unplug the socket, and the alarm couldn't dial out to say it had gone off. In a wires-to-a-wall situation, if there is a random wire cut, the alarm should go into "I have been tampered with" mode. Therefore you can't just drop an inline filter in as easily as you can in front of a telephone. You can do your own ADSL installs (http://jane.nevada.net.nz/realDSL.jpg) but unless you have good equipment, it's not advised. The internet would always drop out at the flat in the picture. :) Craig