Lol I know this is a joke, but I remember reading (on reddit many years ago) about a project someone did where they made the computers in the office broadcast and listen for certain information via infrasound. Something about joining the network or staying on the network or something.

Something about using a similar encoding scheme as that used in GPS signals because it was so low power, but could be picked up in different rooms across the building.

God I wish I could remember the particulars.