Germany says that they will soon launch an app that will use bluetooth to keep track of all the people you are near and to automatically alert you if you have come in close contact with someone who tests positive for Covid-19. And importantly, they say this can be done while protecting your privacy. If that’s truly so: great. I’m skeptical that privacy really can be protected but eager for a system like this. Making it work is going to be one of the challenges of our time for security experts.