Apple today pushed a new version of the firmware for AirTag. The AirTag firmware version released today is 1.0.291, and the version number is 1A291a. Before today, the latest version of AirTag firmware is version 1.0.276 and the internal version number is 1A287b.
To check the firmware version of AirTag, open the Find My app on your iPhone and select the Project tab in the bottom navigation bar. Then, select your AirTag from the list of items, and click the name of your AirTag. Doing so should display the serial number and firmware version of your AirTag. Just make sure your AirTag is within range of your iPhone, and it should update automatically.
It is not clear what is new in this updated AirTag firmware version. Apple has confirmed that it is developing an Android application that will detect AirTags and other accessories that support find, but as of the time of publication, the application is not yet available in the Google Play store.
