Pennsylvania's new coronavirus exposure-notification app is now available on app stores.

Update: as of Wednesday afternoon, at least 50,000 people had downloaded the app, according to the governor's office.

The release of the app, COVID Alert PA, on Tuesday is part of Pennsylvania's effort to more quickly break chains of transmission by using the new technology to notify people who may have been exposed.

The state has a $1.9 million contract, using federal grant dollars, to deploy and maintain the app with software developer NearForm Ltd, an Ireland-based company whose app there has been downloaded by more than one-fourth of that country’s residents.

The app is based on smartphone technology developed by Apple and Google. It is similar to the app rolled out by Virginia last month, when it became the first U.S. state to use new pandemic technology created by Apple and Google. A handful of other states have also launched apps using the Apple and Google technology.

COVID Alert PA and COVID Alert DE don't track users' location, Pennsylvania Health Secretary Dr. Rachel Levine said. The app uses Bluetooth to detect other app users near you. If someone who was near you reports that they tested positive, the app will send a notification.

"It takes one thing that we really never leave home without, which is our phone, and helps us use it to protect yourself and others from this very contagious virus," Levine said.

Once a user gets a notification, they can choose to send their phone number to their state's Department of Health. The user will receive a phone call and can be advised whether they need to get tested. Users can also choose to track their symptoms on the app and search for testing sites.

"If you receive an exposure alert, we actually...will not be able to tell you who you came into contact with that tested positive. It is anonymous. Apple and Google were very specific with building this technology to ensure that your privacy is protected. We won't know who has downloaded the app, who has received notifications, and who has used the symptom check-in. We cannot track that information."

The app will work with the state of Delaware’s app, which released last week, and has 25,000 users, Gov. John Carney said in a statement. Pennsylvania's app will also be compatable with those of other states when they launch on the NearForm platform, state officials say. If a COVID Alert PA user travels to Delaware, the app will work there, and vice versa for a Covid Alert DE user, Gov. Tom Wolf said.

Wolf said he expects New Jersey and New York to launch their versions of the app, which will also be connected.

Use will be limited to people 18 and over.

In addition to exposure notification, the Pennsylvania app has a data feature that allows the user to see up-to-date information on case numbers, hospitalizations and deaths by county, as well a feature that helps the user to monitor their symptoms even if they have not tested positive.

It relies on Bluetooth wireless technology to detect when someone who downloaded the app has spent time near another app user who later tests positive for the virus.

As a threshold, the app uses the Centers for Disease Control guideline of being within 6 feet for at least 15 minutes, state health officials have said.

The identity of app users will be protected by encryption and anonymous identifier beacons that change frequently, the companies have said.

Someone who tests positive in Pennsylvania is reported to either the Department of Health or a municipal health department agency and contacted by a case investigator. That case investigator will ask the infected person if they have the app and if they are willing to use it to notify any mobile-phone users who have been in close contact with them in the past 14 days, state officials said.

If they are willing to use it, they are given a six-digit code to enter to then issue a notification, state officials said.

A person who receives a notification will get something like an alert to check the app, with instructions from the Department of Health on how to protect themselves and others, including information about staying at home, quarantining and seeking medical help.

The identity of the person who was infected is shielded from people receiving a notification, and vice versa, they said.