As previously reported, the UK will break from the Apple-Google “decentralized” approach. Instead, the NHS’s technology group NHSX chose a centralized model, in which a list of contacts made via Bluetooth signals will be stored on users’ devices as anonymous tokens. If a user has symptoms or tests positive, the contacts can be submitted to the app, which analyzes the data and sends notifications if necessary.

While critics say the centralized approach raises privacy concerns, NHSX CEO Matthew Gould told Reuters that the group “put privacy right at the heart” of the app. He explained that the app doesn’t know who users are, where they are or who they’ve been near. Britain’s Information Commissioner Elizabeth Denham pointed out that the centralized approach will allow the UK to gather more insights into the virus, something a decentralized approach might limit.

Just yesterday, France announced that it will begin testing its COVID-19 tracking app beginning May 11th, and Australia has already launched its own version. In the US, a group of senators is working on a bill that would set requirements for data collection and transparency in COVID-19 tracking apps, and Apple and Google have outlined how public health authorities around the world can use their upcoming tracking system to preserve user privacy.

Another potential drawback, is that the centralized approach may eat up more power. Apple’s solution lets the contact tracing happen in the background, but the UK’s app has to be woken up every time the device detects another nearby device running the same software, BBC explains.

By choosing the centralized approach, the NHS is aligning more with Australia than some of its EU counterparts. Australia’s app, which was released over the weekend, uses a mix of Bluetooth and stored contact data on both the app and servers. Germany, on the other hand, has switched its stance and is now pursuing a decentralized architecture, as are Austria, Estonia and Switzerland.

So far, the European Commission and the EU’s data protection watchdog support both models but note that the differences aren’t entirely clear, EUobserver reports. In either case, the challenge will be getting enough widespread adoption for the apps to be effective.