How can I prevent the anti-theft system from engaging while vehicle car is off? on 2006 Chevrolet Malibu Maxx

Car is parked, engine & all accessories off for as long as 2 or 3 hours. Suddenly the horn will start blowing & the lights will begin flashing.

Asked by for the 2006 Chevrolet Malibu Maxx
The anti theft is part of the programming in the computer; There is something, probably due to weather conditions, causing the alarm to go off. A door ajar sensor could be faulty and showing open when it's not open. The only way to be sure is to unhook the battery until some diagnostics can be done. I have seen some under hood fuse boxes fail causing circuit issues, but without testing and duplicating the symptoms it would be hard to say what the cause is.
Thank you.
I have received a faulty "door ajar" message periodically.
That could be the issue.
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