A password key?
Require a key to get into your house?
"The use of passwords goes back to ancient times. Sentries guarding a location would challenge for a password. They would only allow a person in if they knew the password. In modern times, passwords are used to control access to protected computer operating systems, mobile phones, cable TV decoders, automated teller machines (ATMs), etc. A typical computer user may require passwords for many purposes: logging in to computer accounts, retrieving email from servers, accessing files, databases, networks, web sites, and even reading the morning newspaper online.
Despite the name, there is no need for passwords to be actual words; indeed passwords which are not actual words are harder to guess (a desirable property), but are generally harder for users to remember (an undesirable property). Note that password is often used to describe what would be more accurately called a passphrase. Passcode is sometimes taken to imply that the information used is purely numeric, such as the personal identification number (PIN) commonly used for ATM access. Passwords are generally short enough to be memorized."