Apple recently listed the changes to the firmware for in this support document AirTags.
The last version 2.0.36 was just a bug fix, more interesting are the changes introduced in version 2.0.24:
- Enables Precision Finding to help locate an unknown AirTag detected moving with you.
- If your iPhone is awake, a notification alerts you when an AirTag that’s separated from its owner is traveling with you and emitting a sound to indicate it has been moved.
Apple now makes it possible to use Precision Finding on iPhones with a U1 chip (all models from the 11 upwards), i.e. not using Bluetooth for approximate location but the chip specially designed for this purpose. Previously, this was only possible for your own AirTags.
The second change should probably trigger a notification to your iPhone more quickly when a stranger’s AirTag is near you and trigger a sound. It has long been known that the latter is ineffective if the worst comes to the worst.
AirTags are suitable – like other cheap tracking devices – for personal surveillance. The best countermeasures are an iPhone with iOS 16.2 or later. Users of older devices or even Android users can be stalked much more easily with an AirTag, although older iPhones will warn you at some point. Needless to say, surveillance is illegal – however, you should be aware of the possible possibility.