Just wondered if flies hitting the windscreen should make the auto wipers sweep. I always thought it worked by measuring something electrical that water creates (we have a machine in work where the metal level probes touch a plastic pipe. Water presence creates an Electro charge which is then measured as water present)

It can make a windscreen very messy.

Nope, it's done with infra-red light. Thats why flickering sunlight can sometimes confuse the sensor.

Ah,ok thanks.

I'll leave the wipers off during the summer then.