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Americans will celebrate the Fourth of July on Friday, but behind the scenes, law enforcement agencies in big cities and small towns across the U.S. will be on high alert to keep the holiday secure.

This year, the Department of Homeland Security has activated its national terrorism advisory system following .

In Fairfax County, Virginia, the Real Time Crime Center is the hub of police operations. For the Fourth of July, it's all hands on deck, Chief of Police Kevin Davis told Autos News.

"I think I wouldn't be doing my job if I wasn't always worried, but we know our ability to react is better than it ever has been," Davis said.

Police there have the ability to tap into more than 20,000 live cameras across the county, including those worn by officers.

"It puts us in a great position to get additional assistance to the police officers in the street," Davis said.

Nearly 300 officers in the county will be activated on Friday alongside the civil disturbance unit. 

A helicopter and drones will also be on standby.

Assistant Chief of Police Bob Blakely expects large gatherings across the county's more than 400 parks.

"We try to always be highly visible. We believe, you know, preparedness, a little bit of prevention goes a long way," Blakely said.

Officers will be visible on the ground and along the waterways. 

"July 4th is probably the busiest day of the year," said Master Police Officer Tim Judd, who captains Marine Patrol One. "We all work together to ensure a safe outcome."

For families who are nervous to bring their children to their local holiday fireworks, Davis advised, "have a plan, celebrate the Fourth of July and just know that your local police department is here to keep you safe."