He came up with it himself after asking why there was barbed wire coiled around certain gates.

[This was them in the middle of intensive testing for Q's abilities. The boy's mental health wasn't too great even before he was scouted for the mafia, and the additional pressure only solidified his creepy child status.]

This was when it was made clear to him that he wouldn't be able to go out and... play if he couldn't find a way to trigger his Ability without rousing suspicion.