Of all recorders currently available (other than using a phone to record along via a recording app), PR-2 is is least likely of any to set off a metal detector.
That said, metal detection will depend on how the sensitivity of the detector is set. I've seen some cranked up so high they detect as single small coin, even a small washer in a pocket. And others turned down so far they barely detect much of anything.
I just hold it above my head along with my phone and keys as they wand everything else down. No prob. If a walk-through you are paranoid about and don't trust, probably just put it under the phone, keys, wallet and any other stuff that goes in the basket. Its small and square and even with entry-level Jedi skills should be easy to pass off as a phone battery, pager, or remote of some kind if even noticed at all.