A number of banks now allow you to suspend credit cards via a secure app [1] (username/password required). You then un-suspend the card when you want to do it

A number of banks now allow you to suspend credit cards via a secure app [1] (username/password required). You then un-suspend the card when you want to do it and its near real-time. Its not quite what you asked for but functionally its very close. [1] https://www.cardvalet.com/ https://www.cardvalet.com/