The new Shures are made in such way that the device changes the frequency by itself, and that isn't done manually anymore. If you know the allowed frequency range for IEMs in a certain country, then it's quite easy to find an IEM. Usually the IEMs are between 550 to 620 MHz.
In Maiden's case they are in 470-540 MHz range (the usual IEM range is the guitar wirelesses).
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If somebody had an Axient reciever, they could easily log onto one of those frequencies and record the show.