City, state and federal law-enforcement agencies converge on Boston this weekend for a 24-hour "public safety exercise" across the city, but Boston channels its inner Kevin Bacon and yells, "Remain calm!"

Residents in the area may hear simulated gunfire, observe officers responding to simulated emergencies, or see activity in the Boston Harbor. Each scenario will be run multiple times, and organizers urge residents not to be alarmed. There is no danger to anyone in the area, and exercises will be done in cordoned-off areas away from the public.

Why, yes, of course, something this large needs a code name: Urban Shield.

Among the places that will come under simulated siege: The shuttered Circle Cinemas, where local police will stage a simulated bank robbery and "hostage situation."

Other areas in which you probably don't have to worry about whether that gunfire is real: the old B-2 police station in Roxbury (SWAT exercises), the Bowdoin T stop (simulated hazmat spill), Boston Harbor Anchorage #1 (ponder a chemical spill on a ferry boat).

The climactic conclusion will come at UMass Boston, where Transformers, asteroids and the Death Star law-enforcement participants will converge on Sunday for "a culminating exercise involving all agencies and a variety of exercises."

Meanwhile, eight hospitals in the area will be running their own drills for dealing with mass victims of violence and chemical spills.

Participating agencies include regular police from Boston, Cambridge, Somerville, Winthrop, Revere, Quincy, Everett, and Chelsea, SWAT units from several of those communities, Manchester, NH and Staet Police, the Coast Guard, MBTA Transit Police and of course, Homeland Security, which is paying for the whole thing.