Why the NHS contact tracing app could be dead on arrival

On Tuesday, the Isle of Wight became the nation’s Petri dish – the first place to try the NHS’s Covid-19 contact-tracing app. The app is definitely a clever idea: if our phones silently send a unique ID to everyone around us, when we get symptoms the government can alert everyone we have come into contact with. If enough people use the app – the theory goes – we will finally get a grip on the virus, and it will improve our track and tracing capabilities, limiting the spread of the disease. It might even enable us to get back to normal (or normal-ish) life more quickly.

There’s just one problem: the app might not work.

The reason why is technical, but important. For the app to be useful, it needs to be running on our phones all the time – so that it continues to transmit and receive the Bluetooth signals that determine who we have been in contact with. The problem is that both Apple’s iOS operating system, which runs on iPhones, and Google’s Android operating system, which runs on almost every other smartphone, are not designed to work like this.

Unlike a laptop, where if you open up a programme it will stay running until you close it, mobile operating systems have been designed to preserve memory and save battery. If there’s an app your phone thinks you’ve stopped using, after a little while it will be quietly closed.

This means that – especially on iPhones where the app rules are most strict – if you open the Covid app and then have a look at Facebook or watch a video, you might find it silently stops working in the background. For most apps this isn’t a problem – if your photos app has to restart afresh when you open it, you won’t even notice as it will automatically load up the last image you were looking at.