Alarm !! ?

My neighbor's Have Moved out of their house and their alarm for the past 2 week's had done nothing but ring and ring There's no for sale sign outside the house or no way at all of contacting them but whilst I'm at work they or someone keep coming back to reset it leaving and there it goes again its just flashing at the moment and out of knowledge the bell Is a klaxon, flashguard I think as I have the same sort but when the bell stop's you can hear the alarm inside still going

Any ideas on what to do, I don't want to do any illegal stuff but shutting this thing up would be good as it's very hard to ignore it at night

Thanks