the ptc reaches the curie point or the switching point of the ptc material an abrupt change in resistance occurs which shifts the ptc from 300 ohms to approximately 156 000 ohms because of the high resistance of the ptc most of the voltage potential across it drops and limits current flow to bleeding resistor network 20 this causes the alarm to stop making noise even though electrical power is still applied to the alarm circuit through the timing mechanism by changing the value of resistor 18 the 34 on 34 time of the alarm can be changed for example if a higher value resistor is used the value of resistor network 20 is raised and the alarm will have a longer 34 on 34 time referring not to fig2 and 3 there is shown a timing mechanism 140 employing the features of the invention timing mechanism 140 includes a cam means 22 that is fixedly carried on shaft 24 that is rotatably driven by a motor 23 through a clutch not shown in a manner well known in the art the cam means can be manually set by a knob not shown carried on the double d portion 26 of the shaft cam means 22 includes a first set of cams 1 2 and 3 which open and close switches which for the purpose of clarity are not shown these cams and switches control the functions of an appliance which in the illustrative embodiment is a clothes dryer cam 4 includes an outer cam profiles 36 a middle or neutral cam profile 38 and a series of narrow lobes 40 which form a series of notches 41 the bases of which form.