On the bottom of the sock are three textile sensors that measure pressure and where on your foot you place your weight: ball or heel.
The second piece of the puzzle, a separate ankle cuff, fits over the studs. It's this anklet that processes the running data.
It's this anklet that processes the running data, and pairs to your phone over Bluetooth.
If you have one anklet, you'll have to switch off if you're trying to track performance on both feet. You can pair two anklets and a heart-rate monitor to the mobile app.
In order to keep that anklet snug, fold down the top of the sock over the cuff.
Yeah, it bulges and looks strange. It feels a little off-balance, too, but you'll forget about that once you start moving.
The anklet charges through a proprietary charger that looks a little like a mini dog collar.
Once again, those magnets just pull that anklet right on.