Avoidance and evasion

Some drivers use passive radar detectors or LIDAR detectors to detect police radar or LIDAR signals, with the intention of avoiding or evading prosecution by slowing down before entering an enforcement zone. The legal standing of these type of devices varies by jurisdiction. Active devices might also be used-in this instance radar or LIDAR signals are typically jammed with counter emissions. These devices are more frequently illegal than passive devices.

Drivers may flash their lights to approaching drivers to warn them of a speed trap. The legal standing of this action also varies by jurisdiction.

In 2006 the UK Automobile Association controversially published a road map that included the location for thousands of speed cameras-the first time such information was available in printed form, although more accurate and frequently-updated GPS-based information was freely available for some time before that.

(Source: Wikipedia)