points out a report from Ars Technica on how they used a public records request to acquire an entire License Plate Reader dataset from the Oakland Police Department
. The dataset includes 4.6 million total reads from 1.1 million unique plates. They built a custom visualization tool to demonstrate how this data could be abused. "For instance, during a meeting with an Oakland city council member, Ars was able to accurately guess the block where the council member lives after less than a minute of research using his license plate data. Similarly, while "working" at an Oakland bar mere blocks from Oakland police headquarters, we ran a plate from a car parked in the bar's driveway through our tool. The plate had been read 48 times over two years in two small clusters: one near the bar and a much larger cluster 24 blocks north in a residential area—likely the driver's home." Though the Oakland PD has periodically deleted data to free up space — the 4.6 million records were strewn across 18 different Excel spreadsheets with hundreds of thousands of lines each — there is no formal retention limit.