Scraping the bottom of the barrel watch case, we find the pulse-pounding sensor action. And lenses.

Apple's heart rate monitor is actually a plethysmograph—it looks and acts like a pulse oximeter, but Apple isn’t claiming it can measure your blood oxygen level. Why? Beats us.

Nestled in the case we also find a magnet, to help seat the watch on its inductive charger. Electrifying.

We find a familiar looking coil of wire resting in the composite cover. We're guessing this is the inductive charging coil.

Update: Chipworks has identified the Texas Instruments OPA2376 Precision, low noise, low quiescent current Op Amp as part of the sensor package.