An ultra-low power sensor operates using energy harvesting from various sources for efficient monitoring. The oscillator ...

[Alan’s] c ircuit isn’t new, he states right in the video that various audio limiting, compressing, and automatic gain control circuits have been passed around the internet for years.

Yes, it is possible to get sound output from a serial port ... a minute to grab the parts and a second to compile. Mark says audio quality could be improved by using a higher baudrate.