Moving PIR sensor (or IR camera), aka Predator like alien scanner
PIR sensors usually have 2-4 pixels.  That, coupled with the intended optics that appear to be designed with "blind spots" (so something moving in/out of them will cause a change) wouldn't really be that helpful.

As tyblu suggests, an IR camera&mdash;the cheap ones are NIR, not LWIR (thermal)&mdash;may be more helpful, and may even be able to couple it with some FPV (first-person view) goggles for R/C aircraft to make your own hack NVGs.

That said, some FPV goggles and IR cameras can be kinda spendy, so paying just a little more for the convenience (batteries, mechanical package, etc) of some commercial NVGs (or just a scope) might be worth it.