The portable technology is mounted on bike handle-bars and uses an ultrasonic sensor to calculate the distance between a passing car and a bicycle. The device displays the distance in inches and beeps an alarm if the vehicle comes within 36 inches of the bike. A GoPro camera, which is purchased separately, records the vehicle passing and the inches display. This confirms the distance for evidence in court. The city uses billboards and rear-window wraps on patrol cars to educate the public about the bike-passing law. The city periodically uses "stings," which are planned operations in which bicycling officers in plain clothes alert a patrol car waiting nearby to stop an offending motorist. A citation is $120, which includes the fine and court costs. Judges can order a motorist to participate in a 90-minute cycling education class. Austin, TX, has a similar program. In both Chattanooga and Austin, the community response to efforts at improving motorist-cyclist safety practices has been overwhelmingly positive. Community groups in both cities have made significant unsolicited cash and in-kind donations to support increased efforts to make bicycling on public roads safer.