A sensor arrangement includes at least one transparent elevation, which is formed on the surface. The transparent elevation is made of a first transparent material. At least one first facet of the transparent elevation defines a first angle with the surface. This first angle is larger than an angle at which a total-reflection occurs at an interface of the first transparent material and air and is at the same time smaller than an angle at which a total reflection occurs at an interface of the first transparent material and the liquid. A light source is arranged for emitting an incident ray into a first direction passing through the surface into the transparent elevation such that in a presence of a liquid at the first facet, an incident ray is transmitted through the first facet. In an absence of a liquid, the incident ray is reflected due to a total reflection at the facets. A light detector is provided for detecting the reflected ray.