for an external PIR your likely going to need to break out 12v, Ive been using PoE splitters like these with good success:
http://www.amazon.com/iCreatin-ethernet-Splitter-Adapter-Compliant/dp/B00SM196AE/
here is my big black face dahua responding a couple of alarm inputs, one PiR motion sensor and one magnetic contact switch:
then I setup a home automation system, and when a sensor is triggered it sends a command such as this to say: Go to Preset #1, and of course I setup presets for different areas of interest and then do scripts, etc.. when mailbox opens, if any windows/gates/doors within view open/close/tampered with, etc.
Code:
http://username:password@nvr/cgi-bin/ptz.cgi?action=start&channel=1&code=GotoPreset&arg1=0&arg2=1&arg3=0
for things I need really fast response to I use local alarm inputs and also alarm inputs on my NVR.. I can tell my automation system to trigger NVR input #1 and that trigger preset to go to mailbox PTZ in about 1/4 the time as sending the same command via cgi-api.. for somethings that split second response is important, others its not really.. it still responds in about half a second to a second using the command above.