There is a better thing on the market and it's not even bike related...weird why bicycle industry hasn't done a better job especially when considering this, there is a company called TILE that makes a device that is about an inch square and about 1/8th of an inch thick that is designed to be put on your key chain, laptop, or on anything and you can track it anywhere in the world, so a person could use the tile and place it on a bike, and the tile thing is a lot less expensive then the bike specific ones and works a great deal better.
Obviously the challenge would be where to mount it. I think a person could take a TILE and either glue it onto the inside of a crankarm or glue to the underside of the saddle, either area would allow the TILE to transmit. But read this first to find out how it works:
https://9to5mac.com/2013/06/20/tile...ind-lost-items-via-crowd-sourcing-iphone-app/