This is bad idea. A while ago Alipay had this ultrasonic payment method, I queued for a vending machine, opened Alipay in advance because I never used this "ul

This is bad idea. A while ago Alipay had this ultrasonic payment method, I queued for a vending machine, opened Alipay in advance because I never used this "ultrasonic payment" feature before, then just when the guy before me pressed the button, my alipay accidentally payed for him. Luckily he and I wanted the drink of the same price, so he payed for mine instead. Using QR-code or NFC for payment won't mess up like this. And later Alipay completely canceled ultrasonic payment feature. I guess many people encountered the same problem. You can't control omnidirectional ultrasound broadcast. It's very insecure.