If you've ever been concerned about someone unexpected entering your room at night, this Personal Door Alarm may give you the added comfort you seek. It's very compact and easy-to-use.  Also has a push-button LED "key" light.

 

When in your hotel room, close and lock your door and slip the sensor between the door and the jam. Then activate the alarm and hang on door handle inside your room. If the door is opened, a loud 91dB, high pitched alarm sounds. When not in use, the sensor slides back into the alarm.