With their operating systems, Google and Apple build in surveillance for tracking spread of virus
Google and Apple add to geolocation tracking with more detailed tracking of person-person interaction. They will able to track proximity of individuals with Bluetooth. If an individual is COV-19 positive, then that individual and the others would be notified.
They say that the data will be anonymized and stay on the phones and will not collate into the rest of their data. Given the safeguards, this seems like a reasonable response.