It would help to know the exact parts replaced. There was a problem on some of the early cars with one of the alarm sensors being installed upside down. Don't think this is a widespread issue but it's been mentioned before:
Hi fix my 08 in guarrante was the towing sensor intermitent.
But now ar 32k had to replace the shifter motor+ towing=1000.00
Repairs are expensive for this car.
I assume you are talking about the factory alarm? I have a factory alarm on my 08 Passion and so far it is working as it should. Is there a possiblilty that both of your vehicles are subject to some type of high frequency vibrations or someone driving by with a loud exhaust or their sound system cranked way up? Please keep us informed as to how this concern was resolved.
Have a 2008 Passion as well with same problem. Fixed under warranty and probelm returned after warranty. Cherry Hill (NJ) Smart wanted to charge for replacing alarm moduale again. So I don't lock my car anymore.
Occassionally, if I hit the lock button when the key is in my pocket, I need to start the car up and then shut it after a minute to reset the computer.