Kind of like a reverse Portable People Meter:
<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Nielsen_Audio#Portable_People_Meter" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Nielsen_Audio#Portable_People_...</a>