https://www.theverge.com/2018/11/15/18097157/googles-wear-os-update-smartwatch-battery-saver-mode

Google will update Wear OS with several quality-of-life improvements, including the ability to quickly power down your watch and a new battery saver mode. The update is called “H,” and it will roll out to Wear OS smartwatches over the next few months, as detailed in a Google support blog spotted by Droid Life.

With the new update, Wear OS watches will have another way of conserving battery once the charge drops under 10 percent: you’ll be able to turn on Battery Saver Mode and use your watch only to tell time. It will basically become just a regular not-so smart-watch until you charge it again or switch the mode off. The Apple Watch already does this with the Power Reserve mode, and Snapdragon 3100 watches also offer this battery-saving feature.