A keychain is a small chain, usually made from metal or plastic, that connects a small item to a keyring. The length of a keychain allows an item to be used easier than if connected directly to a keyring. Some keychains allow one or both ends the ability to rotate, keeping the keychain from becoming twisted while the item is being used.

A keychain can also be a connecting link between a keyring and the belt of an individual. It is usually employed by personnel whose job demands frequent use of keys, such as a security guard, prison officer, or retail store manager. The chain is often retractable, and therefore may be a nylon rope instead of an actual metal chain. The chain ensures that the keys remain attached to the individual using them, makes accidental loss less likely, and saves on wear and tear on the pockets of the user.

A keychain can also be a short chain used to link together a number of keys or other items.

Keychain items

Items commonly attached via a keychain or keyring include:

• Bottle openers
• Compasses
• Digital sound recorders
• Electronic games
• Flashlights
• Laser pointers
• Logos, slogans, or phrases
• Keyring
• Mace (spray)
• Memo pads
• Ornamental or decorative items
• Personal sirens
• Pill boxes
• Photos (photo holders)
• Religious items (e.g., crosses)
• Tape measures
• Thermometers (analog and digital)
• Tools (i.e., Swiss Army knives)
• Security tokens
• USB flash drives
• Vehicle remote controls
• Watches and stopwatches
• Whistles

By analogy to the physical object, the terms keychain and keyring are often used for software that stores cryptographic keys. Mac OS X uses a password storage system called Keychain.