Is it the principle, or some practicality, of concern?

Maybe have a power control chip with a motion detector , or a normally closed reed switch that you place over a "rest" spot on your desktop, which has a magnet embedded into it.

However, I too have a wireless mouse. I yse NiMH batteries, and just recharge them every couple weeks, so them bein on while not in use is of no concern for me. I have bigger things I need to cut power useage on.

It's not the power usage that annoys me, it's the scramble to find replacement batteries when the old ones die in the middle of a procedure. A simple on off switch on the mouse would solve the problem very nicely.

Mine (a Logitach" comes with software than monitors battry leve, plus the mouse has a low power mode where it occasionally blinks. And I have piles of batteries all over the place.

That really isnt necessary because a wireless mouse uses a very small amount of the battery. I know for my mouse you only have to change the battery every few months.Also the mouse takes so little battery to use mine can even function when i take one battery out.

Obviously a switch would only postpone the panic but since the electric consumption is so minimal it is an unpleasant surprise when the mouse dies in the middle of an operation. I wonder if a light energy recharger might be sufficient to keep a mouse indefinitely operational.

A further extension of the recharging concept would be a mouse that was made like those small portable vacuum cleaners with a dock that keeps the mouse charged when it is not being used.