Hawk & Ox Door Hinge Locks are exactly what we were looking for to increase safety for our students and staff. Installed easily by sliding over the hinges the locks prevent the door from being opened more than a few inches to prevent entry. These are perfect for not only our traditional doors, but also for our Dutch doors with four hinges. The weight of the lock would also make it useful to break a window if needing to escape from the building. In addition, Hawk & Ox is a great company to work with - fast and customer friendly.