[FT] sensors

Reading through other parts of Nyrath's site, I saw discussions of how a
drive plume can be detected from here to Antares, but I didn't notice
anything about how far away you can detect a ship which is using an
Handwavium drive, which (as everyone knows) has no rocket exhaust.  
Let's say you move by generating a small black hole in front of you and
a
negative mass equivalent (generates a push rather than a pull) behind
you.  
a) how would this be detected?
b) how far away could you reasonably expect to detect a ship, just by
its
temperature?

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