Bluetooth is watch initiated, and only turns on 4 times a day (or when the user explicitly requests it with a button press). The pedometer is probably a special chip.

You should compare this with the F-91W that gets 7 years on the same battery, and hobbyist hardware mods that get years out of the same battery running ARM chips.

Nice thing about BLE is that it can be really cheap and stateless, you don't need to keep polling. If it was sending each and every step count to the watch (or even every minute) that would be one thing, but a semi-daily sync for time and steps could easily fit in one BLE packet.

My little temperature and humidity sensors that show an LCD 2x the surface area of a watch and broadcast a BLE packet every minute lasts about 12 months on a CR2032 (~200mah). A CR2016 is ~90mah little less than half. And receiving a BLE packet takes way less energy than sending.

Then you have the on-demand stuff that costs a packet or two, like the lost phone finder -- which is what I'm most excited about.

I had the same thought--speculating, perhaps it's like you say and we'll see a disclosure somewhere that it's "Up to 2 years, with 1 weekly Bluetooth pairing, 1 second of backlight use per day, no step counter."

Though, the CR2016 is a pretty big battery vs typical watch batteries, and in some other Casio watches are used as 10-year batteries.