The sensor allows your wipers to automatically switch on when it is raining and switch off when it stops. Then the sensor adjusts the wiper speed according to your vehicle speed, keeping your view unimpaired by rain.
A sensor on your windscreen is usually attached in the area of your interior mirror, this can also include, light and fog sensors and lane departure / crash cameras.
These pictures should hopefully help you to understand if your vehicle has a sensor / camera fitted.
Rain / Light Sensors
Camera: Lane Change / Departure & Crash Cameras
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