In the early days of the covid-19 pandemic, several competing projects launched around a deceptively simple concept: your phone could alert you if you’d crossed paths with someone who later tested positive. One system for these exposure notifications quickly caught on. It was designed, in an improbable act of cooperation, by Apple and Google, which released the first version in May.
How do the Apple-Google contact tracing apps work?
When you enable exposure notifications, your phone starts using Bluetooth to constantly scan for nearby phones doing the same thing. (This happens in the background, and it’s designed not to use much extra battery.)
When two phones connect, they swap anonymous ID codes. Your phone records how long you spend around the other device and guesses how far away you are, based on a mixture of factors such as how the phone is oriented and how strong the signal from … Read the rest...