1. Open http://borismus.github.io/sonicnet.js/emoticons on Dell 2. Open http://borismus.github.io/sonicnet.js/emoticons on MacBook Air 3. Click on an emoticon 4. Observe the corresponding icon appear on the other system across the room

I made no changes, didn't turn off the music my phone was playing to a bluetooth speaker, etc. This is using the built-in speakers & mics at unadjusted volume levels – the only change I made was unmuting one of the two laptops.