This lightweight and easy-to-use Door Handle Alarm is a security device that transforms an ordinary doorknob into a highly sensitive burglar alarm. In order to gain easy access to you home burglars will first try your doors to see if they are unlocked. Simply hang the Door Handle Alarm on the inside door knob, turn it on, wait 10 seconds and the unit is set. If someone touches your doorknob (from the outside) this device will instantly emit an 85-90 dB alarm (on the inside) to scare them away and alert you to the attempted entry. Even if the would-be intruder is wearing gloves the alarm will sound as soon as the outside knob is touched. It has a sound/light selector switch which allows you to either hear an alarm or see a flashing light when the door knob is touched. The flashing light option is perfect for people who are hard of hearing. For them it can serve as both an alarm and as a silent doorbell letting them know when someone is at the door. The alarm requires one 9 volt battery (not included). It has a low battery indicator to let you know when the battery is weak. It measures 5 and one-half inches x 1 and seven-eight inches (at the widest point) x 1 and a quarter inches (at the tallest point). The strap used to hang the alarm on the door knob measures 4 inches long. Please note that this item will not work with plastic door knobs or on a metal door.