My dog has one on her collar. She got lost once, after chasing a squirrel, so it was a no brainer. The cool thing is that you can make it go off, by pressing a button, and train the dog to come to you when it chirps. I hope I never need to use it in an emergency, but it's good to know I'm prepared.

I have one in a very well hidden pocket in my backpack. Because it’s my gig bag, and goes with me when I’m working in the field. If I were just leaving it under my desk all day, I wouldn’t bother. But since it often ends up sitting in the corner of a random room while I run around a building, it has an AirTag buried in it.