Lost the number when we moved in, is there away of resetting them yourself or will I have to call the guy that fitted it to shaft reset it it for me.

There is sometimes a jumper on the circuit board inside the alarm control unit that will reset the PIN, but it depends on (a) the make/model (not all will have this feature) (b) whether it has been disabled (possible on some systems) (c) whether you’re prepared to endure the alarm going off when you open the control unit.

If you post the make/model of the system someone may be able to provide a more useful answer.

http://singletrackworld.com/forum/topic/burglar-alarm-engineers-lost-code-for-house-alarm-help