Does it work with Android phones?

Only in a limited way. Setup and tracking are built around Apple devices and the Find My app, so an Android phone cannot use Precision Finding or the full Find My network.

How long does the battery last, and can I replace it?

Apple rates the CR2032 coin cell at about a year. You replace it yourself by twisting off the back cover.

Do I need a case or key ring?

Yes, if you want to attach it to keys or a bag. The AirTag has no built-in loop, so a holder is sold separately.

How does Precision Finding work?

On an iPhone 11 or later, the U1 or U2 chip measures the tag's direction and distance and shows an arrow with a range in feet.

It carries an IP67 rating, so it survives splashes and brief immersion, but it is not meant for swimming or prolonged underwater use.

Can I use it to track a checked bag?

Yes. Airlines generally allow trackers in checked luggage, and the Find My network can show the bag's last known location through other Apple devices nearby.