Contact tracing is working in South Korea and Singapore. But it raises privacy issues.

Our cellphones and smartphones have several means of logging our activity. GPS tracks our location, and Bluetooth exchanges signals with nearby devices. In its most basic form, cellphone tracing might go like this: If someone tests positive for COVID-19, health officials could obtain a record of that person’s cellphone activity and compare it with the data emitted by other phone owners. If officials saw any GPS overlaps (e.g., data showing that I went to a McDonald’s hot spot) or Bluetooth hits (e.g., data showing that I came within several feet of a new patient), they could contact me and urge me to self-isolate, or seek a test...

Contact tracing is working in South Korea and Singapore. But it raises privacy issues.

Our cellphones and smartphones have several means of logging our activity. GPS tracks our location, and Bluetooth exchanges signals with nearby devices. In its most basic form, cellphone tracing might go like this: If someone tests positive for COVID-19, health officials could obtain a record of that person’s cellphone activity and compare it with the data emitted by other phone owners. If officials saw any GPS overlaps (e.g., data showing that I went to a McDonald’s hot spot) or Bluetooth hits (e.g., data showing that I came within several feet of a new patient), they could contact me and urge me to self-isolate, or seek a test...