On Monday, 20 April 2015 19:07:18 UTC+1, MM wrote:
Without the casing gubbins around it, this is quite small and compact
enough to mount on the letterbox flap. But the 64,000 dollar question
is, how long could I extend the two wires leading to the buzzer?
The buzzer looks like a small round black drum, approx 12mm dia and
about 15mm long. It has 2 wires coming out of it. It is marked P87J.
How about 3 metres? 10?

Any reasonable distance if the buzzer is the sort with internal driver circuitry and the alarm is only sending DC volts down the wire.

Not sure if it's a bare piezo sounder relying on a driver circuit on the main alarm board.

Owain