The PacSafe Prosafe 750 uses a key card locking mechanism to unlock. To unlock, insert either of the punched corners of the card into the lock slot from the top of the slot without any clearance at 90 degree position. Press firmly until lock snaps open. To lock it, simply press shackle to close. Keep a note of the key card code stamped underneath the key card. Contact PacSafe customer service and quote this key code for replacement. The advantages are that you don't have to keep extra keys with you and you don't have to remember any code.