Go to Activity Monitor, search for blued, and kill the process
With More Detail
At the time of writing OS X 10.10.2 is live and many of the grave problems with Bluetooth have been fixed. Those include
- mouse lag: the mouse was almost unusable for around the first 100 days of Yosemite going live
- audio lag: streaming audio via bluetooth was so poor it was unusable
10.10.3 is about to be released but one serious problem still persists, which is unbearable for anyone who faces it.
If you have a laptop chances are you want to move it from one location to another every once in a while. If you do this on a regular basis, like traveling between home and work, you may even want to have one bluetooth mouse per location, so you don’t have extra junk to carry back and forth. One thing the Mac in its current crippled bluetooth state does not like is connecting and disconnecting two different mice. No matter how many times you switch the mouse power on and off, or search for it in the bluetooth menu in the Mac, chances are it will never be discovered. After huge frustration I resorted to the Windows approach of restarting the whole machine, which basically should never be necessary, and the mouse is discovered right away.
So any easy way to shortcut that remedy, which seems the only way to get multiple mice working on the Mac, is just to start the bluetooth service. A non-tech way to do this is go to Activity Monitor, search for blued, and kill the process. It will restart immediately. Now your mouse will be visible 🙂