Before we crack our watches open, we pull in their predecessor—a.k.a. the Watch3—to look for any differences:

Both the standard and Classic Watch4 models sport sleek, rectangular buttons—rather than the round ones seen on the Watch3.

The introduction of the new Bioelectrical Impedance Analysis sensor on the back of the Watch4 doesn't change the hardware layout. But what’s missing is the service port hatch seen at the top of the Watch3 (third photo, center).