Disable 612 alarm for ferry?

Getting a ferry in a few hours and don't want the alarm going for the whole trip. Handbook says you can disable tilt and motion sensors using buttons near rear view mirror, but sequence of actions is not clear e.g. do you press them, jump out of the car and lock quickly? Or something else?

Or can I just lock with key and not have alarm set?

Thanks, suspected it was that but didn't want to risk it and end up with a flat battery!