I'd love something like a Yubikey Neo (NFC) with a fitness band type form factor (that I can shower/swim with), and an intention indicator (button of some sort) before the NFC would respond.
Right now I use a Pebble smartwatch (which I use for fitness, too) with Bluetooth 4 to unlock my Android phone. Not very secure since (as you put as well) I don't verify the unlock via my smartwatch, and I'm not sure about impersonating Bluetooth 4. Then again, I'm not sure if NFC (RFID) can be impersonated, either. And, if yes, how feasible it is.
