Unfortunately, these devices can also store collected plate data for anywhere from a few hours to a few years, which leads to all sorts of potential privacy incursions by law enforcement. In Oakland, for example, the police used these devices to assemble a database of more than 4.6 million plate numbers earlier this year. Just 0.1 percent of those readings resulted in a traffic stop.

The situation isn't much better in Paradise Valley. When Fox 10 asked town manager Kevin Burke about the devices, he confusingly claimed that the readers were inactive. "We want to make sure we're answering everybody's questions about data retention [and] how the things will be used," he said. "We want to make sure that is vetted before we turn these things up." Which is odd, especially given that on Saturday the PVPD directly credited one of the plate readers with instigating a traffic stop. Burke also asserted that the cactus covers were purely aesthetic. However, UC Berkeley law professor Catherine Crump remains unimpressed. "It seems comical, but given the photo, not exactly an effort at concealment," she told Ars Technica. "I am more interested in what else this town is doing with its $2 million police technology upgrade."

[Image Credit: Fox 10 Phoenix]