Any time an iPhone, iPad, or newer MacBook sees an AirTag, its location is reported back to the owner. Apple devices are so ubiquitous that you can effectively

Any time an iPhone, iPad, or newer MacBook sees an AirTag, its location is reported back to the owner. Apple devices are so ubiquitous that you can effectively get real time tracking anywhere in the developed world where there are people. Similar products like Tile have existed for years, but their real-time tracking abilities are poor because they rely on a network of devices that have their app installed and running in the background.