When Apple Watch was announced last week, like many I was surprised that it didn't include the Touch ID fingerprint security first revealed in the iPhone 5S. But it doesn't need it; and this could be key to awesome value from the Apple Watch. A killer feature. We know that the Apple Watch will need to be unlocked, authenticated, once each day. But that it'll remain unlocked as long as it's on your wrist. However we don't know how it gets unlocked. Tapping in a passcode on the watch screen would be a step backwards after Touch ID. Here's a better plan: we know the Watch needs an iPhone. Place it on your wrist for the first time that day and let the watch communicate with your nearby iPhone for you to confirm your identity, ideally with Touch ID rather than a passcode. Then let the iPhone confirm who you are back to the Watch and it can remain unlocked so long as you keep it on your wrist. Great. But it gets better: once the Watch knows it's securely on...