I ran across this on ebay:

http://cgi.ebay.com/ebaymotors/keyless-entry-door-lock-unlock-No-need-remote-key-_W0QQcmdZViewItemQQhashZitem4aab51a787QQitemZ320701835143QQptZCarQ5fAudioQ5fVideo#ht_2510wt_1149

Here’s how it works. After installing it, if you lock yourself out, you knock your pin number on your window and it will unlock the door. Let’s hope someone doesn’t ride by playing loud techno music!