If you want a durable KISS keychain light I recommend a 1AAA light (Arc AAA, www.arcflashlight.com , or Peak Matterhorn, www.peakledsolutions.com ) over a coin cell light. The AAA lights are metal, built like tanks, waterproof, yet not that much heavier than the coin lights. They run on common AAA cells that are easy to change, and the total light you get per battery is much higher. If you get the Peak unit I recommend the Ultra power configuration.