Once square has linked your credit card is linked with your phone number and email, every time you make a transaction with that card, you get a text message/email receipt.

I suspect you're typical-mind-fallacying.

I don't know how the app works (it might already do some of this), but it would be nice if it would vibrate when you get charged and perhaps allow configuring it for a list of default purchases such that it vibrates twice if it is for a different than usual amount so you don't have to look at it.