Apple Pay, the new mobile payments system that Apple has developed, is secured on the iPhone 6 through the use of Touch ID, but many wondered how Apple was bringing the system to the Apple Watch, which doesn’t have Touch ID.

As noted by Rene Ritchie of iMore and Cult of Mac, Apple Pay on the Apple Watch is secured by requiring a passcode to be entered initially, but once entered Apple Pay would work until the watch is taken off a user’s wrist, then requiring the passcode to be re-entered.

The Apple Watch can detect when it is in contact with skin thanks to the sensors located on the rear of the watch, which are also used to detect the user’s heart beat. It is also backed up by a comment made by Ed McLaughlin of MasterCard who told Re/code that it would use the sensors for security, although he didn’t go into the detail provided by Ritchie and Cult of Mac.

Watch uses passcode to authorize Pay. Authorized for as long as skin contact is maintained. If taken off, need to re-enter pin.

— Rene Ritchie (@reneritchie) September 9, 2014

[Cult of Mac via MacRumors]