SEATTLE (AP) — About 1.6 million people have activated or downloaded the WA Notify smartphone app created to notify people if they may have been exposed to the coronavirus, the state Department of Health said this week.

The app is sending notifications to people who may have been exposed, but the state does not have reliable data on how many times the app has been used to alert people or on how many people have been alerted, The Seattle Times reported.

Part of that is because privacy protections built into the app limit how much information public health officials get and part of it is because the data is messy and filled with possible double-counts or inaccuracies, health officials said.

The app, which the state launched in November, uses a phone’s Bluetooth system to detect proximity of other nearby phones. People who test positive for the coronavirus are given a code to enter into the app. The app then anonymously alerts other users who have been within 6 feet of that person.

“Once you enable it, it’s quietly working in the background of your phone, if you don’t hear anything, that is not a sign that anything’s wrong,” said Lacy Fehrenbach, Washington’s deputy health secretary for COVID-19 response. “No news is good news.”