Do you mean something that simply listens for sound in those frequencies or decodes known signals as well? The latter would be pretty interesting to walk around dense urban and shopping centers with.
Yes, the latter. If this attack is possible ultrasound driving ought to be possible too.
Look for realtime analysis software (RTA) or spectrum analyzer software, typically used for setting up audio systems or analyzing noise sources. One example is RoomEQ wizard. Audacity can do it in non-realtime.