Alarms with auto-dialers and ADSL or FTTC.

Alarms with auto-dialers should not be a problem to ADSL if correctly installed. They just dial a number and deliver an ID to the alarm monitoring service centre, in a similar way to a fax dialling another fax.
It’s a standard telephony device, so it does need to be ADSL filtered. This can be performed with a “BT ADSL filtered faceplate NTE5 master box”, or you can arrange something with micro-filters, but it MUST pass through an ADSL filter or it will interfere with the ADSL.
The alarm should ideally be wired directly to “BT ADSL filtered faceplate NTE5 master box” as a normal extension, although there’s no real functional problem if it’s hard-wired to a secondary extension point elsewhere.
If you have a standard NTE5 master socket and the Auto-Dialler is connected to an extension, then it must be ADSL filtered with a micro-filter.
This means that it’s connected to the BT Exchange Line on YOUR side of the master socket. This is VERY important because it is illegal to connect the alarm system to the BT side of the master socket.
Unfortunately, some alarm installers do hard-wire the alarm connections onto the BACK of the NTE5 box, effectively directly onto the BT Exchange Line, and bypassing the NTE5 master line box which marks the official demarcation point between you and the BT public telephone network. This practice is illegal.\\You are responsible for what’s effectively tampering with your BT line, not your alarm company – so YOU are liable, although BT are unlikely to take legal action against you.
It means that a BT engineer is unable to make an accurate test on the line via the test socket in the NTE5 unit – which is the whole point of the NTE5 type unit.
It also means that no amount of micro-filters or master box adaptors is any use for filtering your alarm if you choose to have ADSL. Without filters there IS an incompatibility because the alarm and ADSL will not function correctly, and quite possibly the alarm will not function correctly.
If a BT engineer is called out to an ADSL fault, and an Alarm auto-dialler is incorrectly installed, it will result in a charge for the engineer call-out and the costs of correcting the wiring, but BT are unlikely to take legal action against you.