I dont think the sensors would detect any movement unless a problem happened. The wheels don't rotate and the movement does not seem to have acceleration high enough to trigger the alarm. Many alarms today don't even get triggered when the car is hit by a ball, for example.

The sound waves from my motorcycle sets them off pretty routinely in parking lots or cars on parked on the street. humorous and oddly satisfying.

This is interesting (never had an annoying alarm)! Seems sound waves create more disturbance for the sensor than an actual blunt impact which is localized to a point on the body and possibly not transferred through the chassis to the sensor.

I don't see how it would be an issue. A parking garage is out of the way anyway so wouldn't annoy anybody nearby. Nobody should be in a giant automated garage so nobody to annoy, and any security threat would be monitored for visually not auditorially.

Not good if the alarm drains the battery though.

Not really a concern unless the cars are being shuffled constantly. It takes a long time for an alarm to drain a battery, believe me I've had some awful neighbors.

It would,but most cars have a way to disable it(in mine if you triple-click the lock button it locks the doors but leaves the alarm off).