Abstract: A domestic appliance such as a clothes dryer having a signalling system including a portable radio receiver transportable by the appliance operator to locations remote from the operating cycle of said appliance to transmit a signal to said portable radio receiver to notify said operator that the operation of said appliance is completed. The system includes an adaptor for releasably and sealingly mounting the sensor unit within the flow exhaust air from the dryer, preferably with the sensing element covered by a screen. The adaptor has an inlet end attached to the exhaust fitment of the dryer and an outlet end attached to the outlet hose.