Virginia Gov. Mark Warner signed legislation prohibiting the sale or use of a device that can change some traffic signals from red to green.

A traffic-light changer is designed to allow police, fire and other emergency officials to clear intersections before they approach. But some drivers have managed to purchase them on the Internet for as low as $100, according to published reports.

People can even buy kits and build the signal changer themselves.

The new law, which takes effect July 1, is intended to deter anyone other than public safety and transit agencies from using the so-called mobile infrared transmitters, or MIRTs.

“Most Virginians don’t even know what one is,” Delegate L. Scott Lingamfelter, R-Woodbridge, told The Daily Press. “My primary goal was to tell Virginians not to waste their money and go out and buy these things because they’re going to be illegal.”

The new law doesn’t dictate a penalty for using the device, so having one would likely become a traffic infraction punishable by a fine of up to $250, the newspaper reported.

The devices, which sit on a vehicle’s dash, are not regulated by current federal standards because they rely on a beam of light instead of a radio wave to trigger the light-changing mechanisms that have been attached to some intersections.

A recent U.S. Department of Transportation survey showed the devices are in use at 26,500 intersections in 78 cities across the country.