where are you? You would be better with a small receiver and glued to Shelly
and a little Ipod booster transmitter you could walk round until you heard
the music playing. Get a small cheep FM radio for Shelly and just tune to
your own frequency. Totally illegal in the UK of course, but who's going to
come looking for you? If your in the UK that would be a cracking project
for some interested ham types but they would be unwilling to break any
rules. legally You could use 446 PMR about £20 a pair and some of them are
tiny.