In a collaborative effort, Apple and Google have developed an industry-standard detection feature called “Detecting Unwanted Location Trackers” (DULT) for Bluetooth trackers. This standard allows users on iOS and Android devices to be alerted if an unknown Bluetooth tracker is monitoring their location.
It has to keep pinging so the iPhone knows it’s still close.
That same pinging is detected by other devices, which is what this feature is about. Alerting you to an unrecognized device nearby that is pinging out.