Intermittant fault on my Citadel XR2 Home Alarm System?

I have a Citadel XR2 alarm system which was fitted in 2004 and which has worked perfectly well up until recently. A few weeks ago the alarm went off for no reason and no indication on the keyboard. I keyed in my code and the "Tamper" light came on and sounder stopped. I reset the system and everything returned to normal. A few days later exactly the same thing happened. This is becoming more frequent, and it could happen 2 to 3 times in one day and then be fine for a day or two. My installer has long since retired so is not available for advice. Any help would be much appreciated.