There are secret messages flying all around you all the time, being transmitted via, most of the time, electromagnetic waves going from antenna to antenna.

Frame taken from the music video for Secret Messages, showing a man with big hair and aviators in front of a big sattelite dish, arms crossed

ELOs “Secret Messages” is a song about posting conspiracy theories via WiFi.

But what if you need to get a few bytes from device A to device B (one of the hard problems in computer science!) and you don’t feel like making sure they’re both connected to the same network? Well, fortunately, another channel is available to us - sound, or for a more fun and less-audible experience, ultrasound.