On holiday last week and in middle of night alarm went off, cancelled it and within few minuets it reset and it automatically armed again. Later on it went off again, went round it and could not see why. In the distance I could here some one else car alarm on and this one also went off several times. Is it possible the heat had got into it and caused this?, any ideas .

An insect fluttering around inside perhaps.

 

If you disable the interior motion sensing you can narrow the source of the trigger down.