A method is provided for operating an apparatus for detecting if oestrus is imminent or present in a milking animal, the apparatus configured to be operated by the steps of: a) defining a processing area which encompasses two or more independent heat outputs including a portion of the rear of the milking animal； b) measuring an indicator of heat output from that area with at least one sensor； and c) using measurement obtained in b) to determine if an oestrus condition is imminent or present.
