Cobra iRadar Detector (High-end)
This isn't really a "smartphone accessory" for your car, but it's something millions should have in their car. Cobra has some powerful and useful smartphone apps too, which work with their different model radar or laser detectors.
What we're suggesting here is the best overall value radar detector for 2019. The Cobra iRadar which works great, has the least false-reports and pairs great with smartphones thanks to a dedicated app. It's over $100, but that's better than getting a huge ticket and your insurance going up. You'll get 360-degree protection or scanning, tons of features, loud alerts, and useful features to make sure you never get a ticket.