During the setup process of an LG G Watch while at Google I/O, I placed it into its charging cradle and the watch powered up. The thought of looking for a power on button or an "on" gesture (since the G Watch lacks physical buttons) never crossed my mind.
Then during my flight home, I turned the watch off in order to conserve battery. I had been testing and using the watch all day and it was sure to die before I arrived home. What I didn't realize was that I would have my work cut out for me to get the watch turned back on.
After repeatedly tapping on the screen, followed by holding a finger on the screen for at least 30 seconds and realizing my efforts to power on the watch were failing, I took my conundrum to Google. A few search results later, I figured out placing the watch in its charging dock was my best bet for powering on the watch. I even quipped about the apparent oversight on Twitter. Little did I know there's actually another trick to turning on the G Watch.
According to Google's support documents, you can also power up the G Watch using the reset button on the back of the watch.
Using a pen, paperclip, or a SIM tool, press the reset button for about 2 seconds and stare in amazement as the watch powers up. You can find said reset button just above the five charging contacts when you turn over the watch.
The moral of the story here is don't make the same mistake I did. If you're going to turn your G Watch off, make sure you're close to the charging dock, or have a paper clip nearby.