Opening the Watch3 is a familiar—and relatively painless—procedure, featuring tri-point screws and a rubber gasket.

These tri-points are tiny, but at least they're captive (hard to lose and easy to re-seal).

While the back cover does feature a booby-trap sensor cable, its ample length makes it fairly benign. No traps were tripped in the making of this teardown.

The ECG sensor, heart rate sensors, and wireless charging coil are all packed tightly into the monolithic back case—but not this freewheeling little speaker, with its nifty gasket.

The optical biosensing is handled by the Texas Instruments AFE49I30.

Texas Instruments TLV9002 1 MHz Operational Amplifier

Modularity is neat! We approve. (Of the speaker, that is. We'll withhold approval of the other stuff until we find a way to extract it safely, which might take time.)