Detect breaches with Canary credit cards
I use Privacy.com, which basically turns every card I use with them into a canary. The first time you charge on one of their virtual cards, they become merchant-locked. No other merchant can charge to that number, and if someone tries, I get an alert.
I have uncovered flaws in online merchants this way, and notified them. They were usually grateful, especially so since the fraudulent charges failed.