The watches' fuel tanks are hidden under the motherboards and nestled within plastic midframes.

Thankfully, both can be removed without any heat—so long as you have a sturdy spudger on hand. (Just don't poke too hard—the usual li-ion battery cautions apply here.)

The Watch4 Classic 46 mm accommodates a 1.40 Wh (361 mAh @ 3.88 V) battery—while its 40 mm little sister, the Watch4, houses a 0.95 Wh (247 mAh @ 3.88 V) battery.

Compared to the Watch3 with 1.3 Wh (340 mAh @ 3.85 V), this represents a modest upgrade. With 1.62 Wh, the 2021 Mi Watch still packs a bit more power—and the Apple Watch Series 6 (44 mm) twiddles its thumbs at the bottom of the stack with 1.17 Wh.

We shake the last components out of the midframe and find a familiar vibration motor next to the barometric sensor.

But the most interesting part is the button flex cable. It not only carries a microphone (#snore-tracking), but is equipped with an additional contact plate opposite its connector. This allows the watch to close an electrical circuit through your body for bioelectric impedance analysis.