If I understand correctly, your car is stalling and you noticed this just the alarm was installed?
Although some alarms do have additional outputs that can activate a fuel pump cutoff, I doubt that that feature is installed unless you specifically requested it. The only wire that is interrupted with an alarm is the starter wire (some Ford locking systems excluded). All other wires are are simply "tapped" into. I can't really say that it is caused by the alarm itself but it could be due to the installation of the alarm. A wire could have been damaged during the install causing the problem.
Can we get some more information?