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When the Department of Homeland Security sought proposals for compact drones for use by U.S. Border Patrol agents, submissions swarmed in — so many that the department stopped accepting them more than two months early.

Originally due to close on July 14, the department’s effort part of its Silicon Valley Innovation Program closed on April 27, according to postings on the government's purchasing board.

"As this was a pilot program, we were hoping to see a robust response from industry, but did not have a specific target [number of bids] in mind," said Ari Shuler, director of U.S. Customs and Border Protection's Commercial Technology Innovation Program. "Our team’s expectations were exceeded as we received more than three dozen proposals."

Michigan State Police Sgt. Matt Rogers and Trooper Don Zinz bring the Aeryon SkyRanger in for a landing during a demonstration of the MSP's new Unmanned Aircraft System (UAS) at the State Police training track on January 15, 2015 in Dimondale, Michigan. Dale G. Young / AP

DHS, through its Science and Technology Directorate, has so far awarded tech startups with more than $1 million, in packages of between $100,000 and $200,000, to develop portions of the miniature drone’s sensor, controller and cybersecurity systems.

That figure could increase by a factor of four or more by the time the drones are ready to fly, since companies are awarded additional funding as they move through each development stage.

Once completed, the drones would be capable of identifying individuals using "facial recognition or other biometric at range," and could track multiple humans on foot, horseback or in vehicles in a three mile range, according to specifications in the federal request for proposals.

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CBP has used drones to monitor the border since 2005. The new drones, which will be small and light enough for agents to carry into and launch from the field, would join the fleet of nine much-larger Predator B drones already operated by CBP.

"A [small drone] operating in proximity to an agent would extend his or her awareness of potential dangers, hazards, and other relevant information," CBP spokeswoman Jennifer Gabris said in a statement. "CBP’s use of [small drone] enhances mission capabilities and supports U.S. Border Patrol agents’ activities, including greater overall situational awareness and detection, tracking, apprehension, and search and rescue operations."

But the addition of facial recognition technology has privacy advocates worried.

"I can understand why DHS is interested in these kinds of drones. Drones are a potentially very useful tool for law enforcement," said Matthew Feeney, a policy analyst at the libertarian Cato Institute.

"The concern I have is drones and facial recognition are two technologies that really could — without adequate oversight — change for the worse the state of surveillance in the United States," he said.

Only those wanted for or with a history of violent crime should be in facial recognition databases, Feeney said.

But according to a report by Georgetown University's Center on Privacy and Technology, more than 117 million American adults were included in largely-unregulated law enforcement facial recognition networks in 2016.

Alameda County Sheriff's Deputy Dave Durbin carries a drone while demonstrating a search and rescue operation on August 14, 2015 in Dublin, California. Noah Berger / AP

There are also concerns about where the Border Patrol drones would operate. CBP’s authority extends past what most Americans think of when they hear the word "border," said Jay Stanley, a senior policy analyst and policy expert at the American Civil Liberties Union.

CBP, the country’s largest federal law enforcement agency, has wide authority to stop and search vehicles within 100 miles of the any external boundary of the United States. Within 25 miles of a boundary, CBP officials may enter private property without a warrant as long as the property isn’t a dwelling.

According to the ACLU that includes coasts, and nearly two-thirds of American adults live in this zone.

Related: ICE Deportation Officers Overburdened, Undertrained: Inspector General

The Border Patrol intends to use the drones "where there is a mission need, which extends to areas other than the southwest border" of the United States, Gabris said, offering the United States' northern border as an example of where the drones could be used. She added the Border patrol will comply with all applicable U.S. government rules and regulations.

Obama-era regulations limit the storage of drone-derived data to 180 days.

"If they were going to be deployed on the border proper — what every American thinks of as the border when you say border — then the surveillance issues are much diminished," Stanley said. "Once you get into areas where Americans work and live, the privacy problems escalate."