Alarm going off for no reason

The alarm has sounded on our Toyota Corolla Sport for the last 4 evenings, the first 3 at 10.45pm and last night at 9.45pm.   We have very recently moved to a noisy area next to railway line and main road, the ca is parked in a private car park away from passing traffic. b The alarm to our knowledge has not sounded in the 14 days prior to this. (To our knowledge, because we can't hear it as we are on the other side of the block: it's being reported by irate neighbours).  In the last month the car has been repaired from accident damage to the front offside wing and side, but we've had it back from that for over 3 weeks now without any problems with the alarm.  Any ideas?

Might be interesting to be in the car park at 10.45 to see whether a train goes past and how fast it is ......

Have you tried switching off the internal alarm system?