You'll need there apps installed:

- AutoWear (on both watch and phone)

- Tasker on phone

- Unified remote on phone (make sure WoL and sleep already work through the app)

2) Set these up in Tasker 

Sending both the sleep + wake command will either wake or sleep the computer... that way you won't need to track if your computer is awake or asleep if you just send both commands.