Apple and Google are giving governments and public health authorities some guidance for designing the appearance of contact tracing apps — or, apps that tell people they may have been exposed to COVID-19 — according to a joint announcement made today.

Apple and Google have said that they will only provide the technical foundations that public health authorities can use to build contact tracing apps. The companies still won’t be building the apps themselves. But today, the companies say that authorities have asked for help with the interface and design.

On a press call, company spokespeople for Google and Apple also shared new principles that public health authorities have to meet to develop contact tracing apps using their technology. Apps won’t be allowed to access location services, which gives developers access to GPS or geolocation data. They also aren’t allowed to use data for target advertising, or anything other than COVID-19 management.

Although the announcement did bring some clarity, key questions about the contact tracing apps remain unresolved.

The companies did not specify which public health authorities are in charge of building the apps, nor which government agencies, inside or outside of the United States, have asked for the app design.

As previously reported by BuzzFeed News, Google told Senate aides that the companies “don’t know” if cities, counties, states, or the federal government will build the contact tracing apps. On a press call on Monday, spokespeople for companies declined to say if they would build them themselves.

The sample contact tracing app images, which were shared with the press, stay true to a few promises both companies have made. Apple and Google have previously said that contact tracing tools on the iOS App Store or Google Play Store would be voluntary, secure, and managed by public health authorities.

Apple and Google shared several sample images that show how a contact tracing app might look. After opening the contact tracing apps, people will see an explanation of what exposure notifications are and how the app will work. The app asks to enable notifications and “COVID-19 Exposure Logging.”

“Your iPhone can securely collect and share random IDs with nearby devices,” the sample prompt for iOS said. “The app can use these IDs to notify you if you’ve been exposed to COVID-19. The date, duration, and signal strength of an exposure will be shared with ‘Sample Public Health Authority App.'”

The sample images also show how COVID-19 test results would be shared. Each person will receive a “unique test identifier” — a string of 10 letters and numbers — along with their COVID-19 test. This identifier would also tell when a person may have been contagious. Typing that code into the contact tracing app gives the app permission to share their Bluetooth beacons — or, bits of code that anonymously show who has been in contact with whom — with their local public health authority. This way, people who may have been exposed can be notified.

After Apple and Google announced they were building the underlying technology for contract tracing apps, they faced skepticism from privacy advocates. But the companies have taken several steps to make their technology secure.

Rather than using geolocation or GPS location tracking, the apps will exchange radio signals via Bluetooth from a distance of about ten feet. The companies will soon give tools to public health authorities so that they can build their own contact tracing apps.

BuzzFeed News previously reported that the companies fear losing public trust by developing the contact tracing apps themselves. But this leaves the difficult task of building a contact tracing app, or contracting developers to build one, up to public health authorities. This decentralization is already creating a system where key app features may vary from city to city, or state to state.

Although estimates vary, some experts have claimed that at least 60% of a population would need to use a contact tracing app to end flare-ups of a contagious disease like COVID-19.

The companies have said previously that after the worst of the pandemic has passed, and when public health authorities say that contact tracing is unnecessary, they will disable the technology that makes the contact tracing apps work. .