Name: Knob-sentry. Descripton:This high-tech security alarm transforms an ordinary door knob into a highly sensitive burglar alarm you can TRUST! Home security is something you should never take for granted. The right device can ensure peace of mind while having ease of use. Knob-Sentry – is a passive alarm device that attaches to door knobs in seconds… Simply lock you door, attach the device over your interior door knob, and turn the power “ON”. The device operates on a 9 volt battery which does not drain until the siren is activated. Siren activation occurs when the knob is turned in a few degrees left or right and will remain on until the power is turned “OFF”. For those looking for an inexpensive home alarm solution in deterring home invasion, the Knob Sentry is a key home security device. There are two versions available, Door Knob and Window Alarm Go to our website ar www.knob-sentry.com for details!