Take it as a sign they’re listening

Watch out. That billboard you’re driving by might be eavesdropping -- not on you but the radio station you’re listening to. This month Alaris Media Network, an outdoor-advertising company based in Sacramento, is transforming its three electronic billboards in L.A. into “smart freeway signs.”

Using sensors that detect frequency “leakage” from antennas, the billboards can read the radio stations that cars are tuned in to, and adjust their advertising to the demographics of the dominant station.

Say most of the drivers on a Friday night are tuned to modern-rock station KROQ-FM. The ad on the sign might change from a Ford Taurus to a Toyota Matrix to more closely match the young, single out-on-the-towners who tend to be the primary listeners during that time period. Now cut to Monday morning drive time and news radio. Presto, the ad will change to something else.

The video boards are on the 710 Freeway in South Gate, on the 405 Freeway near Century Boulevard and the 105 at Prairie Avenue.

But if you’re the only one on the road, don’t expect the sign to change instantly.

“One guy driving down the street listening to a radio station won’t change it,” said Alaris Chief Executive Tom Langeland. “We have to change it manually when we see the demographic profile of the customer.” And that takes about an hour.