That happens in the UK too: there’s the manual test and trace which legally obliges you to self isolate in which case you are supposed to be checked up on.
No-one gets checked up on to see that they're self isolating. There's a shortage of checker uppers on account that they've all been pinged and and fancy a couple of weeks off themselves.
Janzman is incorrect as previously stated.
The app won’t “ping” you just because you’ve visited the same place on the same day. How could it?
However that is why I wondered what happens with manual test and trace: that might well cop you for self isolation, which would be daft, and moreover legally enforceable, unlike the app.