The technology companies said the COVID-19 exposure notification feature will be added to phones in the next updates, but users can choose not to use it.
The system uses Bluetooth technology to track when phones are in proximity to one another. If a user who has opted in to the program tests positive for COVID-19 and inputs the information into their phone, it will automatically notify anyone they've been in close proximity with for an extended period of time.
Only those who have opted in will receive the notifications. The companies say the contract tracing will be anonymous and won't record users' locations.
Privacy experts, though, have expressed concern over how protected users' information will be.
Representatives for Apple and Google said they made the feature native to the phones' operating systems in an effort to expand participation and avoid requiring people to download a separate app.
The built-in exposure notification systems won't interfere with any existing state-run apps that also offer contact tracing information.
Apple and Google first announced their collaboration to build their exposure notification system in April.