I sort of had that happen - I have a cylinder style combination lock with a built on cable that I leave attached to the bike rack at work. That way I don't have to carry it around since I'm just going straight from home to work and back. Theft is really not a problem on our corporate campus and we have security guards so it's just keeping the honest people honest. Anyway, one morning it would not open. There is a way to change the combination and I'm not sure if somehow I accidentally did that or somebody else was messing with it and did that but as I had long since lost track of the instructions and it had no brand or model name on it I was stuck for a while. Then I noticed that it had a patent number and I was able to track down the instruction through the patent number and reset the combination. It's been sitting outside attached to that rack for like 5-6 years now. Still works. I know if I had a key lock I would forget the key and be screwed. As it is I have a spare key lock that I use if I need to run to the store and half the time I find that my wife has taken my keys instead of hers and so I don't have the key anyway.