CityLab reports that police in Chattanooga, TN have developed BSMART, a device to measure whether drivers violate a law that requires drivers to keep a minimum of three-foot distance when passing cyclists.

Using an ultrasonic rangefinder and a display that beeps when the passing vehicle is closer than three feet, the device is mounted on bicycle handlebars along with a video camera to record the encounter. 

Similar laws also exist in Illinois and two dozen other states, but so far, BSMART is used to only issue warnings. Punishment, however, may include completion of a Bicycling 101 course to teach rules of the road that apply to bicycles, or a group bike ride to show offenders how it feels to travel on streets by bicycle. Overall, it's seen as a useful tool to educate drivers and raise awareness of the passing law and already Chattanooga has received inquiries from a number of other police departments about getting their own devices.