"Contact tracing tracks down anyone who might have been infected by a person who was recently diagnosed so those contacts can quarantine themselves and prevent further spread.
To protect patient privacy, contacts are only informed that they may have been exposed to a patient with the infection. They are not told the identity of the patient who may have exposed them.
Google and Apple are working together to use bluetooth to track coronavirus on your smart phone When Bluetooth is turned on, your phone uses radio waves to figure out which other devices are nearby. This could be used to create an anonymous notification network."