You can make an impression of an existing key very quickly. Talking about a few minutes here. This works for all but high security locks. Put the working key in some putty. Makes a three dimensional impression. Let it harden and you are good to go for cutting a copy.
So if you lose access to your keys for even a short time, you are as good as owned. This is true even for secure locks. And you just don't have to lose physical possession of your key. Someone can take a picture of the key and clone it. Experts can just look at your key and figure out how to replicate it.
If you are trying to dup a key, you should try a couple different combinations. One of them is bound to work if you have a little skill. You can take advantage of the possible layouts of keys.
If you cannot take possession of a key, you can use long range photography to get the 411. Software now can even take into account the rotation of a key in a picture.
