A device for detecting a flow of air from an exit end of a tube fed into an entrance end of the tube, including a bore having a first section with a first size bore size and a second section with a second bore size, an obstruction located within the bore between the first section and the second section, the obstruction configured to obstruct air flowing from the first section to the second section, and fixing means to fix the device to the tube so that the bore communicates with the exit end of the tube, wherein in use, an air pressure sensor is used to compare air pressure within the first bore section and air pressure within the second bore section, so that a pressure differential is indicative of an air flow within the bore.