dhenry:
This eBay sensor has active high output.
In that event, run each output, through a diode, to a common resistor to ground and take your signal from that resistor.
The output is high if any of the output is high.
Since the high level is only 3.3V, that will give a high level on the 5V Arduino input of only 2.65V or so. Not enough for reliable operation IMO.