Not that it's likely to help but there are only three possible ways the stock alarm can trigger:
1) Connection of one of the trigger inputs
2) A faulty alarm ECU.
3) A loss of power to the ECU followed by reconnection. The system is designed as such to prevent defeating it by battery disconnection. Course, it can't discern between battery disconnection and other causes of power loss like corroded connectors, fuses, crappy battery cables, bad grounds, etc.
Conditions 1 and 3 require the alarm be armed. Condition 2 does not.