Hacking a handheld radio should let you listen in to every frequency.

[Frank_Stein]

I'd support this with some limitations

For instance, make it part of a construction where you build a little immobile or large radio that can't be easily hidden

Or, if it is handheld, it would occasionally broadcast a bit of static or feedback to cue people that they were being eavesdropped on with hacked radio

I personally like the first option for the potential to also broadcast from it as a pirate radio station