Let me start this off with a caveat. Just as an iOS or macOS beta should only be used on a testing device, not on your daily carry, this AirTag dev mode may have unpredictable results and render your AirTag unusable (though I’m guessing a reset will fix that).

With that in mind, as far as I can tell, you fire up dev mode by tapping the name (upper-left) 5 times.

Here’s a video showing off this debug mode. Can’t help but think Apple will change this over time, but not sure there’s any way for them to update the AirTag firmware, so I’d guess this quintuple-tap will work for the first gen AirTag for life.