Apple and Google Announce Exposure Notification Technology

Apple and Google announced a joint Exposure Notification system in April 2020 to help public-health applications detect possible COVID-19 contacts without collecting a centralized history of everyone’s location.

Phones exchanged frequently changing anonymous identifiers over Bluetooth Low Energy. If a user later reported a positive test through an authorized health app, their recent cryptographic keys could be uploaded. Other phones downloaded those keys and checked locally whether they had observed matching identifiers at close range.

The design deliberately avoided GPS location tracking and kept contact matching on the device. It was an important privacy-engineering example: the system tried to provide useful epidemiological signals while minimizing the central database that could reveal who had met whom.