The input must not be higher than the power rail. For the PICAXE range the power rail should not exceed 5v (recommended) 6v absolute max. Therefore, a 9v signal must be reduced before it is connected to a PICAXE. This can be done very easily using two resistors. If you connect the 9v signal to a resistor of 4k7 and connect the other end to the PICAXE and then connect the second resistor (5k6) between the PICAXE input and 0v it will be OK.
