He is referring to the electromagnetic radiation given off by our electronic devices and specifically the part of the spectrum that lies between 2.4 GHz and 5 GHz. These are the frequencies that carry data between our various wireless devices—WiFi, but also cordless landline phones, Bluetooth devices, and microwave ovens, etc.
To answer your own question – “What if we could?” -RootKid built a device he calls the “Spectrum Slit”, a wall-mounted visualizer that provides a visual representation of ambient radiation levels in the 2.4 GHz-5 GHz band. The signals it catches aren’t just from RootKid’s own devices – as he explains, the device’s antenna picks up signals within a 30-meter radius.
The device is based on something called the HackRF1, a software-controlled radio that can monitor a wide range of radio and microwave frequencies. HackRF1 is connected to a Raspberry Pi, which runs the associated software (written by RootKid himself on a laptop that – in a pleasant French touch – has a full-screen photograph of François Hardy as its wallpaper.) The software monitors the 2.4 GHz-5 GHz band and divides it into 64 segments, each of which is set to control the brightness of a strip of warm yellow LEDs; The stronger the signal, the brighter the light strip will be.
The result looks like a supersized version of the graphic equalizer from a fancy stereo. this is also loud:RootKid explains that coils with separate driver circuits for each row of LEDs vibrate slightly, producing an audible sound, and the rate at which it vibrates depends on the brightness of the LEDs. This means that the pitch of the hum changes with changes in the amount of traffic in the frequency range that a given LED strip is set to monitor; As he points out in a comment, “While running, you can hear every burst of data… really annoying.” (It should be said that in the video, at least, RootKid appears more pleased than troubled by this unexpected development.)
The Full Spectrum Slit is a beautiful piece of wall art and a truly fascinating insight into the world of wireless communications. RootKid’s video follows him as he monitors the device over the course of a day. He observes the ups and downs of network traffic during the day, watching the entire spectrum light up, before various neighbors come home from work.
The video concludes with Rootkid standing in a room filled with warm yellow light, contemplating the device he created. He thinks, “We are surrounded by ghosts of our own making.”
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