Since the festival shooting Vegas hotels have a policy of entering every room every 24 hours. If you skip housekeeping, they get suspicious and then they send security to check on you.
Some clever hackers figured out how to use the phone system to make them think housekeeping had been there[0], so now they do inspections when BlackHat/DefCon is in town because they don't trust their own tracking systems.
[0] One of the hotels had housekeeping dial *5 on the room phone when they entered the room to clean, and then *5 again when they left. So some hackers would put out their "do not clean" sign and then just dial *5 twice 10 minutes apart so no one would get suspicious.
Some clever hackers figured out how to use the phone system to make them think housekeeping had been there[0], so now they do inspections when BlackHat/DefCon is in town because they don't trust their own tracking systems.
[0] One of the hotels had housekeeping dial *5 on the room phone when they entered the room to clean, and then *5 again when they left. So some hackers would put out their "do not clean" sign and then just dial *5 twice 10 minutes apart so no one would get suspicious.