I've had several Hilton Hotels where the clocks are 12 hours off (show 6 pm when it's 6 am and the alarm doesn't ring). The problem with the new clocks is that you have to unscrew the top off the clock to change the time and unless you bring a small philips screwdriver with you, you have to call housekeeping to get it fixed.

I've gotten into the habit of setting the alarm on my cell phone just in case.