A rain sensor for sensing the presence of moisture on a vehicle window, the rain sensor comprising: a sensing circuit comprising at least first and second sensing capacitors (C1, C2) that, in use, are sensitive to moisture on an external surface of a window (1; 10); characterized by the sensing circuit further comprising at least one mimicking capacitor (C int) that is adapted to mimic charging and discharging the first sensing capacitor; wherein at least the first sensing capacitor and the mimicking capacitor (C int) are adapted to be charged, caused by a writing pulse, and each of the first sensing capacitor and the mimicking capacitor (C int) are adapted to substantially discharge, caused by an erasing pulse; wherein the mimicking capacitor (C int) and the first sensing capacitor are configured so that the presence of rain on the external surface of the window in a sensing field of the first sensing capacitor causes a voltage at an output electrode of the mimicking capacitor (C int) to fluctuate in a manner proportional to fluctuation of voltage at an output electrode of the first sensing capacitor, even though the rain is not present in a field of the mimicking capacitor; wherein the rain sensor is configured so that rain is detected based on an output signal from the output electrode of the mimicking capacitor, wherein the output signal is read at least between an end of the writing pulse and a beginning of the erase pulse; wherein the rain sensor is configured so that the output signal from the output electrode of the mimicking capacitor (C int) is converted from analog to digital, and thereafter is subjected to processing for determining whether rain is present on the external surface of the window, and wherein said processing preferably comprises autocorrelation and/or cross-correlation. a sensing circuit comprising at least first and second sensing capacitors (C1, C2) that, in use, are sensitive to moisture on an external surface of a window (1; 10); characterized by the sensing circuit further comprising at least one mimicking capacitor (C int) that is adapted to mimic charging and discharging the first sensing capacitor; wherein at least the first sensing capacitor and the mimicking capacitor (C int) are adapted to be charged, caused by a writing pulse, and each of the first sensing capacitor and the mimicking capacitor (C int) are adapted to substantially discharge, caused by an erasing pulse; wherein the mimicking capacitor (C int) and the first sensing capacitor are configured so that the presence of rain on the external surface of the window in a sensing field of the first sensing capacitor causes a voltage at an output electrode of the mimicking capacitor (C int) to fluctuate in a manner proportional to fluctuation of voltage at an output electrode of the first sensing capacitor, even though the rain is not present in a field of the mimicking capacitor; wherein the rain sensor is configured so that rain is detected based on an output signal from the output electrode of the mimicking capacitor, wherein the output signal is read at least between an end of the writing pulse and a beginning of the erase pulse; wherein the rain sensor is configured so that the output signal from the output electrode of the mimicking capacitor (C int) is converted from analog to digital, and thereafter is subjected to processing for determining whether rain is present on the external surface of the window, and wherein said processing preferably comprises autocorrelation and/or cross-correlation.