A capacitive sensing system (10) is disclosed. The capacitive sensing system (10) includes: (a) A field generating circuit (12) which includes an antenna for generating a capacitive sensing field with a periodic sensing field signal, where the signal includes a plurality of digital pulses, and which is operative to change in frequency and/or phase in response to an object moving within the capacitive sensing field, and (b) A monitor circuit (17) arranged to monitor the sensing field signal, where the monitor circuit (17) includes: (i) A field generator signal counter (22) arranged to count the difference between the number of digital pulses occurring during a cycle of the sensing field signal and a reference value, and (ii) A threshold comparison means (32) arranged to compare the difference value to a predetermined value, and arranged to generate an object detection signal if the difference value exceeds a predetermined threshold value, wherein the monitor circuit (17) is arranged to update the reference val
