I used to have this problem when I kept a SAK Minichamp and a matching Green Inova in my wallet - the thing kept coming on inside the wallet whenever I hit my leg and would be about half dead when I would go to use it. Sadly there's really not much you can do about it because the button switch is so sensitive.

Either store the Inova a certain way where it won't get turned on accidentally, flip the terminals on the battery until you have to use it, or do what I did and replace most of my Inova keychains with Photons, and give the former to family and friends. The Inova keychains are good lights, no doubt, but that's all you can really do.