Midnight settled on Dinah Thompson's Danville home and the thief padded toward her car. The thief pried open the Subaru's door. He found the hidden keys.
He motored out of the driveway and disappeared into the night — a stealthy getaway were it not for one common commuter device: FasTrak.
From the early morning hours of Sept. 22, when her car was stolen, Thompson tracked the thief by logging on to her online FasTrak account. She knew, for example, that at exactly 2:22 p.m. that day, the car thief drove across the Bay Bridge.
And she knew that two days later, at 5:16 p.m., the thief crossed the Richmond-San Rafael Bridge.
For the next week, the thief continued to cross the bridge between Contra Costa and Marin counties — sometimes twice a day — as Thompson viewed the movements from her home and passed them along to police.
``He racked up 4,000 miles on my car,'' Thompson said. ``I couldn't believe he left the FasTrak in there.''
Using the FasTrak time stamps from the bridges, detective Ryan Dunnigan of the San Anselmo Police Department said investigators were able to determine the car thief's general whereabouts, obtain a photo and link him to break-ins and other car thefts that occurred at about the same time he entered Marin County. Thompson's car was recovered.
``It was very helpful she had FasTrak in the car,'' Dunnigan said.
More than 300,000 Bay Area motorists use the FasTrak e-toll device, which automatically deducts money from bank accounts or credit cards so people don't have to stop at toll booths.
Transportation leaders hail the device as the wave of the future, with FasTrak-only lanes on all Bay Area bridges.
But as FasTrak use in the Bay Area rises, the idea of government agencies observing movements stirs debate between crime victims who want to catch a thief and privacy advocates who fear an invasion into the private lives of innocent civilians.
``You always have to have a balance of competing interests,'' said John Soma, executive director of the Privacy Foundation at the University of Denver.
``If there was a legitimate complaint of a stolen car, then the actions seem reasonable,'' Soma said. ``However, if they start crossing the line and start randomly tracking individuals, then I think you have to go back to the classic justification and have probable cause.''
The Bay Area Toll Authority, which manages FasTrak, said it does not give out personal account information to anyone unless police subpoena records for an investigation.
FasTrak's primary purpose in the Bay Area is to pay tolls. But it is also used to monitor traffic flow on most freeways; roadside signals read FasTrak devices as cars cruise by, allowing transportation officials to gauge congestion in ``real time.''
While the toll authority can track toll use for each device, it has no way of tracking FasTrak use away from bridges because the roadside sensors scramble the information and allow anonymity, Rentschler said. There are no programs to unscramble the information, he said.