TORONTO/OTTAWA (Reuters) – Canadian technology firms Shopify Inc and Blackberry Ltd are developing a mobile contact testing app for the novel coronavirus, Prime Minister Justin Trudeau said on Thursday.

The voluntary app is set to roll out nationally after launching in Ontario, Canada’s most populous province, slated for July 2.

The test-and-trace program is emerging as an important tool to identify and contain the spread of the coronavirus, as Canadian provinces gradually reopen their economies after three months of lockdown. On Thursday, Canada officially hit 100,000 cases.

The app will use Bluetooth connections to swap randomly generated codes with other users in a geographic vicinity. Users who have tested positive for COVID-19 will receive an eight-digit number from health officials that will verify their status within the app, which then alerts other users who come into contact with them, according to provincial officials.

“Testing and contact tracing is critical,” Ontario Premier Doug Ford told a separate briefing in Toronto. “Building this capacity will help us stop the virus in its tracks.”

Concerns have been raised around the ability of contact tracing apps to maintain the privacy of users.

Ford said the app, called COVID Alert, is “100% private.”

It was developed by the Ontario and Canadian governments, working with employees from Shopify. It will undergo a security review by Blackberry and will be supported by Statistics Canada staff.

On Thursday, Britain said it was switching to the Apple and Google model for its COVID-19 test-and-trace app after a locally developed system did not work well enough on Apple’s iPhone.