Outcry from privacy advocates prompted Alameda County Board of Supervisors to postpone or possibly scrap plans to purchase a surveillance drone for the Sheriff's Office.

Last minute intervention Tuesday morning by the American Civil Liberties Union prompted supervisors to require explicit authorization to use grant money the Sheriff's Office received to purchase the drone. Now the proposal will have to go to the public protection committee for approval then back to the full board of supervisors. That is likely to happen early next year.

Concern has been mounting among privacy groups for months that Sheriff Greg Ahern was forging ahead without rules for deploying a drone in the skies above Alameda County.

The ACLU and Electronic Frontier Foundation are concerned about the lack of privacy protections. They were dismayed to find that the Sheriff's Office was asking the supervisors on Tuesday to approve a $31,646 grant to help pay for a drone, indicating that the department was far closer to acquisition than they had led the public to believe.

The Sheriff's Office has consistently downplayed concern, insisting that the department has yet to receive authorization from the Federal Aviation Administration and would use a drone for search and rescue missions, such as finding missing children and responding to wildfires.

But a July 20 internal memo from the Sheriff's Office shows the department identified uses other than search and rescue, including barricaded suspects, investigative and tactical surveillance, intelligence gathering, suspicious persons and large crowd control disturbances.

Surveillance and intelligence gathering amount to "spying," ACLU attorney Linda Lye said Tuesday morning shortly before supervisors were to vote on accepting the money during their regular board meeting.

The money was part of a larger $1.2 million grant dispersed through the California Emergency Management Agency.

The item was modified Monday afternoon after supervisors and the sheriff became aware of the controversy building over it. Initially, the wording was changed to allow the sheriff to still accept the $31,646 grant, providing no obstacle to using the money for a drone.

The sheriff is "not taking privacy issues seriously," Lye said.

Undersheriff Richard Lucia told supervisors during the meeting that including the item on the agenda was "an oversight" by staff.

The office will not buy a drone until it has been fully vetted publicly, he said. If supervisors block the acquisition, the $31,646 would go back to Cal EMA or be used for something else if the grant rules allow it, Lucia said, reiterating the office's commitment to a public vetting.

"We stand by our word," he said.

After the meeting, Lucia once again stressed the search and rescue component of the drone. He did not, however, directly answer questions about language in the grant that specifically spells out intelligence and anti-terrorism functions for the unit.

"We're not against drones entirely," said Trevor Timm, of the Electronic Frontier Foundation, which obtained the July internal memo from the Sheriff's Office.

Search and rescue and damage assessment are all legitimate uses of a drone, Timm said. But there is the danger of "mission creep," he said. "We want to make sure the public gets a say."

In fact, Tuesday's agenda item provided few details, describing the drone only as weighing less than 4 pounds, equipped with live video downlink and other related support equipment. And the small Quadrotor model that the department wants to purchase was not among three bids released to the ACLU in November through a public records request.

The manufacturer AirCover Integrated Solutions praised the spindly black four-rotor unit on its website as quiet: at 50 feet it cannot be heard, and at 100 feet it is invisible.

About a dozen U.S. law enforcement agencies already have or are using a drone, including the Seattle Police Department. That number is likely to grow considerably because the federal government has given explicit support for the expansion of drone use for law enforcement purposes.

The FAA is responsible for developing safety guidelines but has not kept up with the need for privacy rules. No federal guidelines exist for how data collected by drones can be used. The International Association of Chiefs of Police developed recommendations for the use of drones, but they are not compulsory.

"We should not be rushing headlong into buying a drone without guidelines," Lye said.