OAKLAND, Calif.—Weeks after Ars published a feature on the scope of license plate reader use, the Oakland Police Department unilaterally and quietly decided to impose a data retention limit of six months. Prior to April 2015, there had been no formal limit, which meant that the police was keeping data going as far back as December 2010. That puts the OPD in line with other jurisdictions, including the Drug Enforcement Administration, which decided in 2012 that it would reduce its license plate reader (LPR, or ALPR) retention period from two years to six months.