It would require user to press some kind of "Stop!" button, when receiving device goes off - then, it should be possible to check last, lets say, 5 codes used (to re-try each one separately, checking which one really worked).

To be effective, it would require sending codes not-too-fast - something like one or two per second. I think, that it would still make browsing through dozens of keysets *much* more easy.

/Estel