Those with auto wipers

I thought this was a "trick question" kind of thing.


iPhone ?

 

Was wondering how it knew it was raining.

 

I wonder if it can tell the difference between bugs and rain... wiping bugs with the wiper always made a huge mess on my other cars

 

I didn't look into the Prius one at all but my other cars use infrared beams (I think of different wavelengths). Those beams are aimed at an angle to the windshield where it bounces back into a light sensor looking for that specific wavelength. When there are water droplets on the windshield the light refracts at a different angle, missing the light sensors so the wipers activate. Wrapping your fingers over the sensor is blocking the light so.....

If you leave it on auto all of the time sometimes when the sun is at low angles the wipers will go because the light is being washed out so much the sensor can't distinguish what it's looking for.

 

I would have thought the OP fingers were wet and that activated the wipers.
Then again I wonder, how did those fingers get wet?
haha