Hi, there are several possibilities that could be causing the alarm to go off & the first step in diagnosing the problem is to have the car checked for fault codes & too see what the most recent alarm triggers have been stored. A common problem for false alarms can be a faulty alarm siren - this has its own tamper circuit & when faulty can give false alarm triggers.
If this is the case then there will usually be fault codes stored for the alarm siren or the most recent triggers will be with the siren
There are of course many other possibilities which is why a diagnostic check should be carried out first
Best regards, Paul