Us English say "tripped", meaning the electricity/lights have gone off. The actual word "tripped" in this context means an open circuit. Open circuits can't conduct electricity. If an alarm gets tripped, it has been set off. In your example, if the alarm has been tripped (set off) and the cause is unknown, it's got a fault somewhere.

I would say that "tripped" in this context does actually mean the same as "triggered". Unless the alarm was triggered by some electrical fault, which might also be described as "tripped". For example a circuit-breaker "trips" when the current becomes too large, which means it disconnects the circuit in order to prevent wiring becoming overloaded.