StreetWise 72-4130 130 dB Personal and Door Alarm with Flashing Light There are many different ways this alarm can be used a personal alarm or a purse or briefcase or backpack alarm Using the included door clip you can use this item as a Door-window alarm With the included door clip you can also use this item to protect your laptop computer from being stolen As an added deterrent an alarm warning decal is included Unit operates on one 9 volt battery (not included)