One of those details is the ability to remove the battery of the tracker and change it. It has been suggested that the battery used would be one of those small circular batteries that you might use in a watch, meaning that you should be able to replace the battery easily and buy it from pretty much any store.
It also seems that users will be able to set “safe” locations. This means that should the device that the accessory is tracking end up in any of those locations, users won’t be notified of it. For example, you could setup safe locations in your home so that even if you’re out of range, like the tracker could be in your room but you’re in the kitchen, it won’t alert you. Instead, it will alert you if it was outside the safe zone.
Last but not least, MacRumors discovered an image of the accessory in an internal build of iOS 13 suggesting that this could be what the accessory looks like. It is unclear if this is a placeholder or if it could be the real thing, so take it with a grain of salt for now.