This is what I currently have in the car - REI sells it for kayaks but it's also designed for road safety.
This is a worthy research subject. The Power Flare is intriguing so I may get one to try out and compare. And I may also carry a traditional flare, or two. Redundancy in this arena has merit.
http://www.rei.com/product/785182The
Seattle Sports HydroStar S.O.S. Deluxe light features a bright
xenon strobe light, a suction base and a magnetic socket.
* Mounts easily to boat decks of fiberglass and plastic kayaks; magnetic socket
attaches to the side of a car for roadside safety lighting * Attaches to a PFD to become a personal safety beacon; features a handy attachment clip and cord
* Waterproof to 50 ft.; includes batteries