Waking from Interrupt 0 happens when an external interrupt edge is detected on the INT0 pin. INT0 can be configured to be active high or active low. The example circuit shown is for an active high INT0 pin. A push button is used to pull the INT0 pin high briefly while a pull-down resistor normally holds the pin at a low state. To reduce switch bounce sensitivity, a capacitor can be added to low pass filter the signal.