does any one know what this button is for?

Looks like it turns off the low-speed noisemaker - the sound which alerts pedestrians that a silent car is approaching. Otherwise knows as the Vehicle Proximity Notification System (VPNS)

On cars for the US market there is no option to turn it off, but in other countries there is.

 

Hey, welcome to Prius Chat
I concur, it is for enabling/disabling the noise maker in other markets than global North America.

 

Nirmal, your picture is not working.

 

argh! i wish we had one of those!

 

If the switch is there outside US, might the wiring be taped to the loom some where behind the dash?

 

it's possible. we need one of our intrepid diy'ers to go looking. most everyone seem to be disconnecting the speaker. i don't think anyone was aware of the possibility of wires being there, this is the first i've heard of a switch.

 

i don't know what you get there, but european and u.s. are different.

 

I believe the idea of the external artificial engine noise (aka. VPNS) was originated from Japan. In Tokyo or other big cities in Japan, side streets are much narrower than those in North America cities. There are a lot more pedestrians fighting for space with the cars in narrow streets. A lot of pedestrians complain that they couldn't hear the hybrid cars coming from behind. So comes this invention.

 

Yes sure.
That's the exact function. Someone doesn't like the strange sound though it's for safety.

 

Had a person walking in the parking lot today right in front of me and they didn't even pay attention to the noise. I guess the best noise is a nice loud air horn.