Hellschreiber is a broadcast piece based on the Completely Automated Public Turing test to tell Computers and Humans Apart. With the World Wide Web as a predominant realm of communication and networked culture, the relationship between human and artificial intelligence has produced some curious phenomena. A fairly common one is a set of puzzles which attempt to distinguish between humans and bots during authentication processes: the "Completely Automated Public Turing test to tell Computers and Humans Apart", popularly known as CAPTCHA puzzles. CAPTCHAs tend to make their content as little machine-readable as possible, usually via bitmapped versions of text, smudged or superimposed letters, etc., thus making it hard for automated scripts to read, but relatively easy for humans to infer. A common case is Google's reCAPTCHA service, visually very similar to the product of Rudolph Hell's low-bandwith transmitter: the Hellschreiber.

A little-known aspect of CAPTCHAs are their audio versions. In a strive to make web content accessible to blind users, audio CAPTCHAs have to resort to a variety of other means of obfuscation: puzzles would consist of spelling challenges, voices would be garbled or filtered, background noise of different kinds would be introduced, etc. The juxtaposition of so many different audio signals results in something very similar to a well-known part of ShortWave culture and history: the Numbers Stations. In the case of Numbers Stations, again, the guiding principle seems to be similar: maximum propagation and accessibility via short wave broadcast, and a strict, encrypted code, only accessible to a few select individuals.

Long past the heyday of the Cold War and Numbers Stations, audio CAPTCHAs present a strange, little-known soundscape, hidden from view and from most people's attention.

Except for those who are out there, listening.