"Lockdowns" secure and limit access to buildings. In the school environment, lockdowns may require students to return to classrooms, or in the most serious situations, restrict students to the classroom to keep them out of harm's way. Lockdowns may be an appropriate action to contain a violent incident, to restrict entry by a violent or armed individual, or even limit access by an estranged parent or spouse in a domestic situation. Lockdowns can only be effective, however, when appropriate physical security barriers are used. Four types of locking devices are best suited for school lockdowns: the mortise level lockset with security classroom function, the cylindrical lever lockset with security classroom function, the rim exit device with security deadbolt function and auxiliary trim, and the double-cylinder exit device. The mortise level lockset with security classroom function has three modes for differing levels of security. In "passage" mode, both levers retract the latch bolt; in minimum-security mode, the outside lever remains rigid while the inside lever retracts the latch bolt; in the maximum-security mode, the outside lever remains rigid when the deadbolt is thrown, preventing entry. When the deadbolt is engaged, entry is virtually impossible. The cylindrical lever lockset with security classroom function features a deadlocking latch bolt by lever on either side; it allows locking of the outside lever from either inside or outside, protecting students and teachers while securing their classrooms. A key must be used on the outside to retract the latch bolt, lock and unlock the lever, and to lock the door from the inside. The outside lever remains locked if the inside lever is actuated. The rim exit device with security deadbolt function and auxiliary trim has a secure solution for doors that require exit devices. The double-cylinder exit device allows a teacher to lock the door from the inside without leaving the room, thus eliminating the chance of exposure to outside threat. This article concludes with advice for replacing existing locks and exit devices with classroom security locks.