An anonymous reader writes with news that a California Senate Bill would authorize the state's Department of Motor Vehicles to test a digital registration plate system patented by San Francisco-based Smart Plate Mobile on as many as 160,000 cars. An article on the proposed trial in the Modesto Bee says, in part: "The state hopes the technology will improve efficiencies in vehicle registrations and potentially save the DMV some of the $20 million spent each year in postage for renewals. Privacy advocates say the approach could leave motorists vulnerable to government surveillance by undoing a Supreme Court ruling that required authorities to obtain search warrants before using vehicle tracking devices. 'It means everyone driving in California will have their location accessible to the government at any time,' said Nate Cardozo, a staff attorney at the Electronic Frontier Foundation. In 2010, the Legislature considered a similar bill supported by Smart Plate Mobile, with the noted addition of allowing for scrolling advertisements when a vehicle comes to a stop for four seconds or longer." If only it took smart plates to track you.