The top of the Tinder HOT Box Solar Fire Starter was also serviceable as a signal mirror, which is a great side benefit and one more reason to have this in your survival kit. This solar fire starter is 2.625 inches in diameter, .725 inches thick, and it weighs 4 ounces. It is made from rugged aircraft aluminum, and it's easy to handle with its knurled grip. The only difficulty in using this device is finding the right zenith and azimuth to hold the mirror. Just a moment of trial and error will get you lined up, though, and you'll know it's right when the smoke starts rolling off the tinder. The HOT Box retails for $39.95, and it is both fun and effective to use.