Do you drive more in the city or on the highway? Highway drivers usually want the most sensitive detector possible -- one that will give them the earliest warning of a looming speed trap, so they'll have time to brake from high speeds. City drivers may prefer a "smart" GPS-equipped detector that blurts out fewer false alarms from urban and suburban radar sources (like automatic door openers). Only really expensive models, like the Best Reviewed Escort Passport Max (Est. $550), excel at both.
Do you drive past speed or red-light cameras? GPS-equipped radar detectors have built-in databases (updateable, if you buy a subscription) of thousands of these cameras nationwide, so they'll warn you whenever you approach one. As of September 2013, 521 communities have red-light cameras and 136 have speed cameras; check the Insurance Institute for Highway Safety's website to see if yours is one of them.
Do police in your area use laser speed guns? If so, even the most expensive radar detector probably won't help you. Laser beams are just too small and precise. Every radar detector in this report can detect laser guns -- but usually not until it's too late. However, laser jammers and anti-laser sprays can baffle police laser guns; see our section on laser jammers.
Do you need an "invisible" radar detector? Probably not, experts say -- unless you're running your radar detector illegally. Radar detectors are perfectly legal in most places in the U.S., but Virginia and Washington, D.C., have outlawed them. Federal law bans them in commercial trucks over 10,000 pounds, too. Police radar-detector detectors (RDDs) can spot most models; only a few are completely undetectable, like the Escort RedLine (Est. $500).