How to shut my house alarm up?

We bought a house with an alarm system already fitted - unfortunately the previous occupants were deceased and the house was empty so we had no instructions for it except the code. Anyway the alarm panel randomly beeps every so often, generally during the middle of the night. The problem is the contract for the alarm expired many years ago, theres no manual with the alarm and the company who fitted it want an extortianate amount to come out and look at it. Someone on their help line said "its probably the battery", but that was all. I know they probably have us over a barrell, but would this battery be in a sensor and could we replace it? The panel looks pretty tamper proof (ie theres no obvious screws to be able to take it off) but we are at the stage where we would just like to take a sledgehammer to it. To be fair if I could cut the wires to the loudspeaker on the box outside (ive had the cover off and although thats a bit noisey it looks fairly straightforward) then I would put a hammer thru the control panel! We dont really have any need for the alarm as we never remember to switch it on anyway plus our neighbours are great at keeping an eye on the place, most of them being retired. Anybody got any ideas of switching the alarm system off? I know perhaps its not knowledge that should be in the public domain, but the things driving us nuts BUT we dont want to pay a company over a hundred quid to come out and switch of their product in our house which we dont want.