Fingerprint scanning repeatedly
I'm missing a datasheet on that sensor, but here is a hunch:

The sensor is capacitive, meaning, once someone puts the finger on it, it will charge a capacitor on the device. 

This makes me think there has to be a way using this capacitor being charged as an interrupt signal for the micro controller. This way you won't have to continuously poll it.

Here on eBay a capacitive sensor:



The wakeup signal goes high when a finger is detected.

As for the signals you posted earlier, I have not been able to identify such a signal. Maybe the sensor you are using only supports polling.

OPTICAL SENSOR FOUND EARLIER

I made a quick search of some other fingerprint scanner and found this. This one is optical though

By looking at the documentation in this link, I see the following signals are available: