Police use of a technology that allows officers to tap into cell phone communications is raising privacy concerns.
Officials said the so-called "stingray" device mimics a cell tower and tricks wireless devices on the same network into communicating with it.
"Stingrays create serious privacy concerns because they collect information about the devices and whereabouts of innocent third parties, and not just the target of an investigation," the American Civil Liberties Union of Northern California said in a release.
Documents released by the ACLU, originally obtained through a public records request by KXTV in Sacramento, reveal five Bay Area law enforcement agencies all have or have received grant funding to obtain stingray technology. The agencies are San Francisco Police Department, San Jose Police Department, Fremont Police Department, Oakland Police Department and the Alameda County District Attorney's Office.
Some of the agencies received funding to buy the stringray technology as early as 2007.
The Oakland Police Department said it has access to the stingray device and its technology.
"It is used to assist us in a variety of investigative strategies," Oakland Police Department said in a statement.
An OPD investigative report shows the agency made 21 electronic surveillance or stingray arrests in 2007
NBC Bay Area is unable to determine how much the department paid for the stingray device, but a 2009 invoice reports the OPD paid more than $13,000 for maintenance.
In addition, documents also show the department won grant funding for stingray devices in 2011 and 2012.
The ACLU is now pushing for more answers about when officers are using stingray and if they have a warrant to do so.
Bay Area residents have mixed reactions to police using the stingray device.
"You don't want your freedoms taken away, but you also want to be protected," said Rachael Cortez, a San Francisco resident. "It's so hard."