Another simple alarm that can be used in your home or even a motel room is to put an empty glass jar upside down on your doorknob. This will fall (and make a loud noise, except on carpet) should someone turn the doorknob. (Warning- the bottle can break leaving glass fragments on the floor). A soda can filled with loose change balanced on the doorknob will make a lot of noise if someone attempts to enter. Windows also easy to trap with cans of change or jars.