I had a Clifford concept 600 on my pug 306, Mine use to go off all the time when the binman would stop his truck right next to my car on purpose so the proximity warning alarm would go off....i think it humoured him no end...
Also when it was very windy this would set it off. Try taking it back to where the alarm was fitted and get them to reduce the sensitivity of it.
Im sure you can alter the sensitivity with the keyfob...i was given a print out how to do it from the place i got mine fitted, as its not in the manual. I will have a hunt for it..
Sometimes after driving in the rain then putting the alarm on i would get 4 chirps...the alarm sensing that the bonnet was open....basically the sensors dont like water, could be a possibility some water has got to them.