Entry times can be recorded... recall that the company pays for the hotel room and thus ownes the data... the above poster is correct in terms of a company investigation... usually tied to drinking on overnights...
The company will ask when the crew member was in the room for the night... the company has a record of the times... the truth will set you free...
Also, if you are close to the 12 (or 8) hour rule, don't pay with a cc. Pay cash. If the credit card machine isn't time stamped properly or the wait staff waits too long to run the card, and you "pay" inside the 12 hour rule and the company has a reason to investigate, this will seal your termination. It doesn't matter if you stopped drinking an hour before 12(8) and been sipping water...
Regardless don't drink inside the rule...
Finally, back to room keys... always keep your key... if you show up at the airport and the flight is delayed for hours just go back to the hotel and chill. It is allot easier than trying to ask scheduling to send a new hotel authorization....