Amazon used Echo devices for all kinds of invasive purposes other than advertised. Tracking the bluetooth identifiers of nearby devices is small potatoes compared to other things they've done:

https://en.wikipedia.org/wiki/Amazon_Sidewalk

One of those purposes was to explicity use Echos for tracking purposes:

> Amazon’s partnership will allow it beef up its tracking network, called Sidewalk, by letting Tile and Level devices tap into the Bluetooth networks created by millions of its Echo products.

https://www.cnbc.com/2021/05/07/amazon-partners-with-tile-to...