This is a locksmith tip that might save you some dough if you're ever locked out.

Make a photo copy of both sides of your house (this won't work for cars) key. Keep them in your wallet/car whatever. It won't do a criminal any good unless they have a library of key blanks and is also especially handy with the file

Rather than charging to go out and fix your locks the smith will be able to use your photo copy and a set of depth keys to make you a new key without ever having the original. It just involves measuring with some calipers.

This can save a ton of money considering what smiths charge per hour.