The ProSafe 750 uses a key-card locking mechanism to unlock: a credit card sized key sits in your wallet, so you don't need to carry extra keys or remember a combination. The card's punched pattern is unique and coded, so should you lose it, you can contact PacSafe for a replacement.
It may sometimes be the case that security staff need to check your bags before they join you on the plane. To avoid your locks being broken and thus rendered useless, PacSafe's Travel Sentry approved locks allow TSA agents (US) and HRSC officers (UK) to open and relock your bag using codes and secured tools.
As an alternative, you may prefer.....