Apple and Google are expanding their digital coronavirus exposure notification system so that it can notify people even if they haven't already downloaded an app for the purpose, potentially expanding the adoption of the technology.

Why it matters: The companies say 25 U.S. states and territories are exploring digital contact tracing options. Just six have already launched apps.

Details: The "express" version of the technology, announced Tuesday, pushes a message to iOS and Android users in participating states letting them know that they can opt in to exposure notifications even if authorities in their area haven't built an app.

• As with the app-based system, the express version uses Bluetooth to identify which phones have been in close proximity for a defined period of time — data that can then be used to notify people that they may have come in contact with an infected person. Public health authorities still get to set the parameters for what constitutes an exposure.
• iOS users can get notifications without an app. On Android, users will be sent to the Google Play Store to download one that Android can generate on the fly if there isn't already an app available locally.
• As with the regular version, the system doesn't collect location data or share identity information with other people, health authorities or Apple and Google.

The big picture: Apple and Google said the express version is primarily aimed at boosting adoption in the U.S., though other countries could use this approach as well.

• More than 20 countries have already launched apps using the Apple-Google technology, including Germany, Switzerland and Japan, the companies noted.
• A number of states and territories are expected to support the new express option, including Maryland, Nevada, Virginia, and Washington, D.C.

What they're saying:

• Apple and Google, in a joint statement: "Exposure Notifications Express provides another option for public health authorities to supplement their existing contact tracing operations with technology without compromising on the project’s core tenets of user privacy and security."
• Maryland governor Larry Hogan: "Exposure Notifications Express will help to save lives, greatly enhance our contact tracing operation, and advance our statewide COVID-19 recovery.” 

Go deeper:Apple, Google limit how coronavirus contact-tracing tech can be used.