What is the round "button" on the dashboard

The light sensor to adjust the brightness or your speed display and/or switch on the automatic headlights.

 

Except in the US, there is no option for automatic headlights on/off, nor automatic changing of the dash display.

This has been evident on both my old 2005 Prius and my 2010 Prius. What a waste...why install it if they don't use it?

 

It is a solar sensor for the Automatic Climate Control (at least in the US). The Automatic Climate Control will use this sensor to determine the intensity of the sunlight hitting the car and the current position of the sun relative to the heading of the car. If you have the A/C in auto mode, the system will adjust the fan speed, compressor speed and recirculation mode depending on data collected from the (humidity sensor, outside temperature sensor and solar sensor). If you want to try out the sensor do the following:

1) start the car in your garage or covered area. (very noticible around noon)
2) set A/C on automatic mode around 75 degress
3) leave the car for 3 minutes or so to get the interior cool down.
4) when the computer lowers the blower speed and switches to outside air (re-circulation mode off). Drive the car into direct sunlight.
5) you will notice the A/C will immediately react to the sunlight (increase blower speed, recirculate mode will be engage).

 

No,no,no!!! It's a belly button...used for naval maneuvers.

 

How does the sensor "sense". Is it infrared, visible, etc. I have Llumar AirBlue 80 tint on the front glass and hven't really noticed a differance in functionality (almost always in in auto ac mode).

 

pls beam me up

 

I guess it is most accurate to say that it is a multi purpose sensor for several things, some of which we have on our cars in the USA and many of which we don't.

 

So....can I tap into this sensor for an auto headlight mod???