Analog Pin Behavior

So, I have a necessity to use an analog pin to act as the input for a PIR that outputs 3.3v logic. Other projects I have seen like this use a digital pin, and with the analog pin I do not seem to get the kind of switching I hoped for. Perhaps this the scenario that calls for the pull up resistor function? Perhaps there is a threshold in analogRead I can use?

Any consultation is greatly appreciated!

Analogue pins are digital pins with the added functionality of analogue-in.

pirState = digitalRead(A0); // will work for a PIR sensor

Leo..

Thank you!