The device, the size of a shoe box, is tough to spot unless you make a habit of looking skyward to inspect utility poles while driving.
But in 14 locations around the Washington area, the devices are there, sensing which radio stations drivers are listening to by picking up faint electronic signals emitted from car antennas as they drive by.
Car dealers, many of whom have embraced the MobilTrak radio device, above, believe that 80 percent of their business is with customers who live or work within 10 miles of a car lot.
The technology, owned by MobilTrak Inc. of Phoenix, was introduced in this region in May. By year-end, MobilTrak hopes to mount nine more units to monitor the listening habits of more than 1 million drivers and present the results to advertisers eager to better reach the audience in the country's eighth-largest radio market.
The monitoring aims to help retailers choose where to advertise by giving them a snapshot of which stations consumers tune into as they drive by their businesses. The most enthusiastic MobilTrak adopters: auto dealers, who generally believe that 80 percent of their business is with people who live or work within 10 miles of a given dealership.
"It's all about precision marketing," said C. David Boice, 39, MobilTrak's managing partner. "It's about giving marketers real-time data about what's happening in certain areas at certain times so they don't waste their advertising dollars."
The approach is the most recent example of the powerful ways marketers are using technology to track customer behavior in natural settings. The strategy in slightly different form is already well entrenched in supermarkets, which track customers' purchases with loyalty cards. Much to the alarm of privacy advocates, technology is helping marketers identify their ideal customers, such as the frequent buyer of a certain brand of detergent, and fine-tune their selling.
In this case, privacy advocates are not too worried because MobilTrak does not collect identifiable data about a car or the person driving it. It cannot see or eavesdrop on the driver. MobilTrak compares its technology to a rubber hose laid across a road to count traffic.
Its solar-powered units randomly pick up signals across six lanes of traffic from cars up to 140 feet away in the same way a police officer measures car speeds by pointing a radar detector at traffic and repeatedly resetting it.
Still, one privacy expert called the technology "creepy" while another raised concerns about the potential of combining it with other technologies to create more intrusive marketing techniques.
"It would be a quick leap to connect that data with other data," said Barry Steinhardt, director of the technology and liberty program at the American Civil Liberties Union. "Technology is moving at the speed of light. We've reached a point where there are few technological bars to doing anything."