If there is not an On/Off switch, or a feature in the mouse to automatically go to a low power mode, then just open the battery area of the mouse and remove all the batteries.
I'd typically think that just removing one (if there are two batteries) would be sufficient, but I have one mouse that seems to use one battery for the scanning LED, and the other used for the associated reading circuitry. So removing ALL of the batteries will positively reduce the power usage to ZERO! ![]()
It's a chore, to be sure, but if you are bothered by the consumption of the batteries... a minor task.
I have a Logitech Cordless Optical Mouse and was wondering how do you
turn it off????
I always have to replace the batteries at least twice a month.
I hardly ever have to replace the batteries for the mouse I use
with my netbook and the one I use for the laptop because the have an on and off switch on the bottom.
I'm tempted to buy the mouse I'm using for my netbook that's made
by Tech Universe because besides having an on and off switch it's
the easiest of the 3 mouses I have to replace the batteries in.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic