Nliiitend1 is correct. (google it) The sensor projects IR light through the windshield at an angle, then detects the amount of light that is reflected back. Water on the windshield will cause different amounts of IR light to be reflected back, but anything that causes light to reflect back similarly to water could trip the sensor.
There is nothing about the sensor that is chemically specific to water.
This is probably why they always do a double sweep. The wiper itself is reflecting back an IR response and the system is calling for another wipe.....(limb)
I mean double as in double. Wiping the windshield twice. Two cycles. I can put a drop of water on the sensor with a dropper and they will cycle twice. Up/down (once) then up/down again (twice). It will do this nearly 98% of the time I've done it. Doesn't matter where the sensitivity setting is.
Annoying as hell with driving in light mist. They always sweep two times regardless of how light the mist is.
They have used panty machines in Japan --in fact they have more vending machines per cappita than any other place on earth . You can even buy cars from a vending machine and negotiate with it !
You could get in the habit of turning the auto on whenever it's starting to rain.
Personally, I'm doing that because in the winter time the last thing I want to happen is have the wipers go while there's tons of ice on the windshield!
I find mine go into "retard mode" or full speed sweep way too easily. I would prefer a simple adjustable timed setting and low/high speeds. I almost never use full speed even with the Florida downpours.
