That the umbrella pairs
Not when a $5 bluetooth-LE proximity tag will do the same job. And when your umbrella is wrecked, move the tag to the next one.
The tag can even beep if your app detects you are leaving and rain is forecast. Sorry to wreck the slashvertisement.
You're right, a small $5 solution is better than a fragile $105 solution. I stand corrected.
I'm not sure if I ever saw somebody admit to an error in
"If it's not loud, it doesn't work!" -- Blank Reg, from "Max Headroom"