A pair of tethered drones built by a local company will hover over the Boston Marathon starting line in Hopkinton for the first time as part of a high-tech security plan targeting low-tech terror attacks.

Built by Danvers-based CyPhy Works, the Persistent Aerial Reconnaissance and Communications drones, or PARC for short, are tethered to the ground with thin wires, letting police survey the crowd with cameras equipped with long-distance zoom, electro-optical and infrared capabilities.

“The wire provides power so it can stay up for days, and days, and days, it doesn’t have to come down,” Perry Stoll, CyPhy Works vice president of product and software told the Herald. “It can send unhackable, secure communication up and down the tether as well. It’s perfect for public safety and security where it has to be up for a while.”

CyPhy Works provided PARC drones for the 2016 Tokyo Marathon. The drones can track moving targets and fly in all weather.

“It’s really something new we’re going to be using where we have a very dense population of people between the village and the start line,” Kurt Schwartz of the Massachusetts Emergency Management Agency said during a marathon security briefing yesterday. “They will not be over spectator areas, and they will be providing live video feeds into public safety command centers.”

Last month’s deadly assault in London involving a knife-wielding assailant driving an SUV is top-of-mind for law enforcement officials as they prepare for the fourth marathon since the 2013 Boston bombings.

“The attack in London brings to the forefront how rudimentary the planning process may be to be able to conduct a successful attack and cause devastating results,” FBI Special Agent-in-Charge Hank Shaw told the Herald. “All it could take is a car, or a knife, or a sharp-edged weapon or a gun. It can be as simplistic as attempting to run people over.”

Shaw expressed confidence in the six months of planning that have gone into security for the annual Patriots’ Day event, which is expected to draw more than 30,000 runners and as many as 1 million spectators, but concerns remain.

“There’s going to be vulnerabilities, you can’t harden everything, you do the best you can with the resources to get it done,” Shaw said. “All contingencies and concerns have been addressed, but what concerns me most is what I don’t know.”

Boston police Superintendent William Ridge said Department of Public Works trucks would be used in designated areas from Audubon Circle in the Fenway area to the finish line to prevent cars from being able to drive into the crowds.

More than 5,000 law enforcement officers will be dispatched along the marathon route. State police Col. Richard McKeon told the Herald there are currently no known threats against the race which is “fairly typical, but it doesn’t allow us to let our guard down either.”