I FFT incoming sound buffers, and if the 2KHz band is the highest for a suitable number of consecutive frames, then I send the email and stop listening for a few minutes to avoid double notifications.
2KHz is the frequency of my machine's beep. Just triggering on overall noise level alone would notify me each time the machine goes into spin, but using the FFT allows it to be more discerning.
I hacked together an Android app specifically for the purpose, so it doesn't really answer the original question about generally available projects. (I haven't got round to releasing the code as it's rather bespoke, but could do if you're interested.)
I have my old Galaxy S1 sitting in my cellar listening to the beeps from my washing machine. It sends me an email when the wash finishes. (I can't hear the beeps from upstairs.)
[1] https://www.youtube.com/watch?v=uRJ-fPAO3Go [2] https://play.google.com/store/apps/details?id=com.figmentano...