I have LiftMaster MyQ Garage Universal Remote Controller (821LM). Is it possible to create a rule that triggers the alarm if the garage door is opened?
To trip an alarm you would need an alarm sensor on the door which is compatible with the panel you use. A tilt option for the IQ Panel 2 would be the RE106.
There is no way to use the MyQ system or MyQ tilt sensor to trigger alarms.