Dutch Covid app sends 10,000 notifications per day

The Dutch government's coronavirus notification app CoronaMelder has been downloaded 3.7 million times and sends around 10 thousand notifications per day, Ron Roozendaal, chief information officer at the Ministry of Public Health and in charge of the app, said to broadcaster NOS.

The idea behind the app is that it keeps track of close contacts using Bluetooth technology. If someone tests positive for the coronavirus and reports it on the app, the app will send a notification to all other app users who were within 1.5 meters of that person for longer than 15 minutes during the period in which the person was contagious. 

That works out in most cases, but there have been some incidents of the app sending a notification at a further distance, Roozendaal said. "In the vast majority of cases, the app recognizes the distance correctly. But in a small number of cases you were at a greater distance." About 70 percent of notifications were correct. About 20 percent received a notification if they were between 1.5 and 3 meters from an infected person - a 'safe' distance, but still relatively close. The remaining 10 percent were between 3 and 10 meters away, the maximum reach of Bluetooth.

The app measures the strength of the Bluetooth signal to try and estimate the distance between app users. There are some variables here that could interfere with that, including whether you have your phone in your pocket. "If you have two telephones on a table 2.5 meters apart, and one of the two belongs to someone who has tested positive and also uses the corona app, you could well receive a notification," Roozendaal said to the broadcaster. "If you have it in your pocket, that chance is a lot smaller."

According to NOS, there are stories on social media of people claiming they received a notification when they were not near anyone. "That is very unlikely," Roozendaal said. "We sometimes also hear stories from people where the app seemed to pick up the signal from the neighbors, but that is very few." This happens when neighbors are on either side of a hedge, very close to each other, for example. "And we also know a story that the signal would have passed through a window."

But in most cases, you were close to someone who had the virus, Roozendaal stressed. "At least 15 minutes and in any case close together. So that's why the advice applies: if you get a notification, go into quarantine."