In the late-1970s while still at uni I was as a sideline working on a project for water-companies who were starting to use 5-tone selective-calling: both to define individuals/call-groups of user radios in their voice-radio vehicle nets and also for early experiments in polling 'digital outstations' that when triggered would send back their status and data [river/outfall flow rate, for flood predictions] using a train of 5-tone data-blocks.
[The 'outstation' radios were a version of the low-band Pye Europa designed to be wall-mounted, fitted in little brick-built cabins beside rivers and sewage-farms, and connected to a box of digital-fun based around PLL tone-detectors, a bit of TTL and a 2708 EPROM that defined the particular outstation's ID]
This was the time when the movie "Close Encounters of the Third Kind" had just been released - and yes, as chief geek I had my personal 5-tone code as the Close Encounters theme,
https://youtu.be/-JpIjv6XSLM
which caused some amusement when the system was demonstrated to a bunch of high-level Whitehall types!