The sensors I bought on ebay, the operating voltages that they stated in the spec says 3.3 to 5.0v I have them operating at 12v without issue which is the voltage that I want to switch them off at,the 9v supply was the pp3 9v that I used to see if the circuit would operate ok which it did but as soon as I used the bench supply at 9.5v the sensors switched on when as you know should be off ? I have followed all the suggestion to no avail, I will give the circuit you gave Misterbenn and see how that works the weekend. Cheers