Near-Field Communication (NFC), is useful for lots of things, such as automatically unlocking your Android phone when you pick it up. You can wear your tag like a ring, or even paint it onto a thumbnail. Adafruit's Becky Stern explains how in this video.
We've shown you how to unlock your computer and automate rooms in your house with NFC -- there's no reason that your phone shouldn't also be able to know its you as soon as you pick it up. Luckily, it's easy to set up if you have the right components. Becky Stern (who just stopped by for an interview you should read) walks you through the project in the video above.
You'll need a phone that supports NFC (and most popular Android phones do), and an NFC tag to unlock your device. You'll also need to root and customise Android to support polling for NFC on-power, as opposed to after-unlock, but the Adafruit Learning System guide below explains how to do all of that. It also includes the APK required for the tweak. All you'll need to do once you're rooted is install it.
The guide walks you through each of the wearable NFC tag projects in the video, whether you want to go the easy route and just wear a tag glued to a vending-machine ring, try the 3D-printed ring with the tag embedded or go all-out with a thumbnail tag. Hit the link below for the full walkthrough, as well as more suggested uses for NFC/Tasker.
Unlock Android Phone with Wearable NFC [Adafruit Learning System]