A police officer violently bangs on a classroom door with a sledgehammer, knocking off the latch, but the door barely budges. He repeatedly wedges a breaching tool into place, prying the door from the side and from beneath, but the metal doorjamb inside the classroom holds. No one, at least with conventional tools, is getting in.

The officer’s efforts are part of a promotional video for one of the many classroom barricade devices that have hit the market in recent years. The devices differ in design, but most attach to the inside of a classroom door or frame, and all have one basic objective: to keep active shooters or other potential attackers out of a classroom.

Source: NFPA