I am uncomfortable keeping client's key codes though in some instances it is necessary.
If I must store keychart info I prefer storing it as a computer file and I store it encrypted. My favorite encryption program is "TrueCrypt," which is open source and free, though a donation is nice. (http://www.truecrypt.org)
TrueCrypt allows you to do a couple neat things:
1) You can triple encrypt, with up to three different encryption algorythms;
2) You can encrypt whole drives or just files;
3) You can require a second "key file" (a picture of your kid for example) be present in addition to your password;
4) You can store the program and the encrypted file on a USB drive and run it anywhere you need to (at a client's site for example);
5) It's PC, Mac and Linux compatible;
6) It is a constant work in progress and is always being debugged, updated, refined and improved...
No, I don't get any money from them, I just have used the program for years and love it! You could also look at "KeePass" (http://www.keepass.info). It is not as feature rich, may be less secure but is simpler to use. It is designed for storing internet sites, user names and passwords and includes a "notes" section. I think it could be used for storing locksmith info pretty simply.
I also use blind codes for doing simple key code encryption. I use a two dimensional chart to come up with the code. Each side of the chart uses a ten letter word. A letter is selected from the column to identify which line is used for the rest of the cipher.
X L O C K S M I T H E
B 1 2 3 4 5 6 7 8 9 0
L 2 3 4 5 6 7 8 9 0 1
A 3 4 5 6 7 8 9 0 1 2
C 4 5 6 7 8 9 0 1 2 3
K 5 6 7 8 9 0 1 2 3 4
H 6 7 8 9 0 1 2 3 4 5
O 7 8 9 0 1 2 3 4 5 6
R 8 9 0 1 2 3 4 5 6 7
S 9 0 1 2 3 4 5 6 7 8
E 0 1 2 3 4 5 6 7 8 9
CHIKOEL would decode as: Fourth Line, Code #207534
I don't keep this code but give it to the client, and not on the back of a business card! In an address book, a cell phone, a day planner, even on the inside of a kitchen drawer, just someplace they can find it again and bring it in or read it to me over the phone...
TODB
PS: If you know any other ten letter words without repeating letters, I would love to know them...