HOUSTON (AP) — Ominous music plays as a man in dark clothing, sunglasses and a backpack walks toward people working in a high-rise building. The narrator's voice warns: "It may feel like just another day at the office, but occasionally life feels more like an action movie."

Moments later, the man opens fire on a security guard near an elevator.

It's the beginning of a nearly 6-minute video created by the City of Houston in an effort to teach residents what to do during a shooting. Local Homeland Security officials said they realized during training exercises that first responders knew how to react but citizens were far less knowledgeable.