The UK's Covid-19 contact tracing app asks users to scan a QR code when they enter certain places.

I suspect that scanning the QR code immediately informs the state where the phone is located at that moment. That is a violation of people's privacy.

The Google/Apple contact detection protects privacy pretty well, though I am not an expert on it. I'd be willing to use that, if it did not require a mobile phone.

Italy has an approach I think is better, both for finding all cases and for respecting privacy: simply test all the acquaintances of anyone that catches Covid-19, and don't worry about whether they saw each other recently.