Alarm going off and flashing the tamper light?

Since Sunday our alarm has started going off on it own, at all times of the day. Once around teatime, once through the night and once in the morning.When we go to the control pad the tamper light is on. We turn it off using our normal 4 digit code it turns off . We have not had any work done to the house or messed with any of the censors. What could be causing this and how can we stop this from happening

Kate
June 2010