Depends on the frequency and protocol being used by the hardware.
Try bottom of this
page to see what I mean about the frequency; different
hardware is tuned to different frequencies. Don't know if there is an
'all-band' scanner, but it's not likely to be cheap.
b/g are definately 2.4Ghz, a is 5.8Ghz, while N can be 2.4 and/or 5.8
depending on mfr support.