scantronic 9651 alarm fault?

The alarm was fitted 3 years ago when the house was built,
one year ago it started going off even when unset, the alarm company cleaned the hall sensor and everything has been fine since then, until now. The alarm when set, is now triggered by the kitchen sensor and the warranty has run out. Is it possible to repair these by yourself or will I have to call someone out to look at it, if so how much should I expect to pay?