They find out somebody has the virus. They track that persons movements. They identify the citizens who were in the same locations around the same time and notify them. Don’t be paranoid. We’re at war. It’s an emergency.
Sure and if that was the only way to do it, I'd be okay with it in the short term. But I'm just saying that it's a lot less intrusive and narrowly tailored to just get people to write names and phone numbers down at stores than have 24 hour a day 7 day a week tracking using your phone.