I know this won't help you much at this point but I have three keys to every bike I own. I keep one at home, one I ride with and the last key stays on a ring attached to my belt loop. The key I ride with has a ring connected to a small caribiner. When I get off the bike it goes straight to my belt loop. I ride too far too often to be able to afford losing a key. This also may be a very dumb question but did you check your trunk seat release? Not questioning your intelligence but I see it all the time. If I was a bike thief I could have "owned" a few bikes in my time, lol.