In the Bluetooth preferences, it’s the box checkmarked “Allow Bluetooth devices to wake this computer.”
Also, I say it’s unintelligent that this feature is turned on by default because for notebooks, it’s useless. Usually when we sleep our notebooks, we close the lid. On a MacBook, opening the lid wakes it back up automatically. There’s no need to use the Bluetooth mouse to wake up the notebook. This setting should certainly not be turned on by default.
MacBook users? If you own a Bluetooth mouse, disable this setting now.
Ahhhhh – so this is why my Macbook keeps waking up from sleep whenever my Logitech V470 bluetooth mouse goes to sleep (thus initiating the “lost connection” dialog, and waking up my Macbook).