Some of it is conducted the old-fashioned way, by workers who interview those who test positive for the coronavirus, ask them about recent contacts and then contact those people. But it’s predominantly done via a National Health Service “Covid-19 app” that residents can download onto smartphones. If a user tests positive for the coronavirus and agrees to it, the app uses Bluetooth technology to identify other users who in previous days came close enough to the infected person for long enough to be at risk. The app then notifies those people and asks them to self-isolate for 10 days. Isolation is mandatory only in the case of the old-fashioned method, not with the app. In any case, it’s not required to download the app, and since the start of the “pingdemic,” thousands of users have deleted it to avoid having to risk isolation. There are reports that the app is overly sensitive, for example identifying neighbors as contacts through house walls. Another complaint is that users are asked to isolate even if they’re fully vaccinated. That rule is set to be lifted only on Aug. 16.