Legally police need evidence of some crime (probable cause) to stop and investigate an individual. This is so police can't just randomly confront people or even worse illegally discriminate based on race. Police have historically used minor traffic violations like tail light failure, the smell of marijuana, or "furtive movements" as loopholes to the requirement of probable cause. A technowiz device provides an excuse to just stop and frisk everyone near the alert even if the cause was a car backfiring.