Change detect

I am trying to get the Xbee to read a change detect from a piezo film detecting movement. I have it cascaded through two transistors with an NPN feeding the D0 pin. If I really bang on the piezo I get a change detect. If I tap on it slightly I can see (through the LEDs) that the development board receives a transmission from the remote Xbee but no data comes through as indicated by the terminal. I am at a loss for why this is. I have tried to add a cap to the D0 pin incase the pin change was too fast but to no avail. Is there something in the Xbee or development board that causes this? Thanks.