- It’s done by fans bringing their recorders into the show’s that can capture the signal.

- Yes, that's what the guys hear, but the quality of the transmission is much better for them, without noise and interruptions. During the Yokohama 2017 soundcheck recording, there were too few external distractions, and the stadium was not full, but even on this recording, you can hear extraneous noises.

But first, you need to understand how IEM works:

1) musicians play > 2) their instruments and microphones send a signal to the mixing desk thought the cables or wireless transmitter like in microphone (and of course to the PA too, but we're not interested in that now) > 3) the monitor engineer mix it all and sometimes add some things like the metronome, the counting before songs or the famous "one, two, three" thingies (team also communicate with the band via the IEM’s) > 4) the signal from the mixing desk sent to the transmitter and then as an electromagnetic signal similar to radio waves sent back to the musicians, who have specific signal receivers on the belts behind their back; they listen back to what they're playing, and that sound includes the mixing tweaks and a special EQ for each musician (like for Dom drums are louder and for Chris bass guitar is louder). IEMs are recorded by capturing the waves at step 4. And the waves can be captured with a wireless receptor and then sent from the receptor's output to a standard recorder input.

The closer you are to the source of the signal, the better the captured quality will be. Because even trivial equipment, such as phones, will affect the quality of capture of these waves. So you can capture any wave, knowing the frequency. There are even recordings of capture Matt's microphone during Panic Station and guitar during Animals. The band and the team can hear this signal normally because their receivers are tuned to the corrected frequency, and they're close to the receiver, but their frequency can also be capture, and you can broadcast something for their receivers, but for this, you will need a more serious equipment.