Chris Conley, an attorney whose work with ACLU Northern California focuses on privacy and technology, said the best practice is to keep the data for as short a period as possible and to limit access. Tiburon, for example, keeps information from automated license plate readers for only 30 days unless it relates to a specific criminal investigation.
"The law enforcement value of old records not retained in connection with any specific investigation is extremely low, while those records continue to pose a privacy risk to individuals," he said.
Attorneys investigating wrongful convictions for the Innocence Project had a different take. Some told the media that old data helps determine whether the right person was arrested for a crime.
Retention isn't the only issue raising concerns with privacy advocates. Menlo Park, like many other agencies using automated license plate readers, would pool its data with other jurisdictions that could access the information with a username and password, said Menlo Park Police Chief Robert Jonsen.
In effect, that compiled data can function as a type of GPS tracking without a warrant. Mr. Conley said that poses a privacy risk because the data lets law enforcement construct a comprehensive record of someone's activities — for example, is a car regularly seen at a health clinic? How about a protest or church service or job fair or speed dating event?
"These issues are exacerbated if information from (automated license plate readers) is shared with other agencies or combined with other data sources to build an even more detailed record of innocent Californians' legitimate and even constitutionally protected activities," he said.
Chief Jonsen said he understands the concerns, but the courts have held that there's no expectation of privacy for vehicles on a public street. Officers already run plates manually, and log the inquiries; automation makes the process faster and captures more plates.
"The readers have been really valuable, in my past experience; that would apply up here as well," said the chief, a 26-year veteran of the Los Angeles County Sheriff's Department. "Sometimes we don't know about a crime for weeks or months, and it would be a shame to not have the data."
— Sandy Brundage