Yerp I've been caught out by a business before.
They installed the alarm. 3 weeks later it kept going off. Their installer looked at it and said he didn't know how to fix it. And that was it. Brilliant. Stuck with an alarm that goes off for funsies.
Ended up going to Action Alarms in Osborne Park (No sure where they are now?) and they put a whole new system in. Best alarm ever.