Yeah... Tile... It helps you find things... or others find you...

I want one, but it's scary. The new one even has batteries.

From the Verge article above:

Tile was an early Kickstarter success story and now it's hitting the big leagues. Starting today, there's a new version that will be available both online and in retail stores. The Tile is designed to help you find your keys — or purse, or basically whatever else you can attach it to. That remains unchanged — pair it to your iPhone or Android device and you can tap a button on your phone to make the little square dongle beep. Tile says that said beep is three times louder now and will work within 100 feet — both claims ring (ahem) true in my testing. Tile also has another clever feature — if you lose something, you can tell the Tile hive mind and every Tile user's phone will start looking for it. If it's detected, you'll get an alert on your phone — but the user who came near it won't know, protecting your privacy and your stuff.
Every phone can become a Tile now

Tile has also updated its app, now it lets the Tile system ring your phone if it's lost, effectively creating a backup find-my-phone system

And if there's any doubt about how it works, and how much it lives in the background...

On Android, one sort of annoying thing about the system is that you can't quit the app if you want it to work. That does mean you can kill it and save battery, but it seems like the sort of thing that ought to live in the notification tray.

 Welcome to the unwelcome part of the future...