1. A presence detection system for detecting objects which move through an entrance of a space, comprising: a light source for emitting invisible light; a plurality of sensors for receiving the invisible light emitted by the light source; and a sensor processing unit for creating a signature of a moving object; the presence detection system being arranged such that, in use, a subset of the sensors receives the invisible light upon movement of the object through the entrance, and such that the sensor processing unit creates the signature based upon the composition of the subset, wherein the plurality of sensors comprises a two-dimensional array of sensors mounted substantially vertically in a frame of the entrance; wherein the two-dimensional array of sensors comprises at least a first column of sensors and a second column of sensors; and wherein the sensor processing unit is arranged to determine whether the object enters or leaves the space by monitoring the chronologic order in which the sensors of the first column and the sensors of the second column receive the invisible light, characterized in that the plurality of sensors further comprises a one-dimensional array of sensors mounted in the frame substantially perpendicular to the two-dimensional array of sensors; wherein the sensor processing unit is arranged to determine the height of the object by: determining a distance value indicative of the distance between the object and the frame based upon signals generated by the sensors of the one-dimensional array, and calculating the height of the object using the distance value and signals generated by the sensors of the two-dimensional array.