Tag your umbrella as "lost," and the app will notify you when you come back into the Tile's range. If you just leave it behind somewhere, you can locate its last known location on a map.
In Orwellian fashion, you can also search for your missing umbrella by tapping into the phones of other Tile users. Tile tells me this happens without those users' knowledge, but that they consent to it when they agree to the app's terms of service.
As Tile's website puts it, "Every new member that joins Tile adds another 100 feet of finding power."
I really like the Blunt XS Metro + Tile. If you'd prefer to keep track of a more traditional "stick" umbrella, check out the Blunt Classic + Tile for $99.
A Tile's battery lasts about one year and cannot be replaced--you just buy a whole new Tile (currently priced at $25, with discounts if you buy in quantity). But don't forget that buying into the Tile ecosystem means other uses will be able to use your phone's resources to track their missing stuff, too.
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