The National Health Service (NHS) has launched its long-awaited COVID-19 app in England and Wales. Problem is, the app doesn't work on iPhone 6 and earlier models of the smartphone.

So, what does the app do? Firstly, it provides contact tracing using Bluetooth and it also allows you to input your postcode district to check the risk level in your area. The app also has a "QR venue check in" feature, as well as a symptom checker and test booking option.

The exclusion of Apple's older smartphones from the app rollout could pose accessibility issues for people with low income and the older generation, who might not have the latest model. The app requires handsets to have Android version Marshmallow 6.0 (released in 2015) or iOS 13.5 (released in May 2020) as well as Bluetooth 4.0 or a more recent version.

The app is also only available on smartphones — not tablets, smartwatches, or any other devices. If you've got an iPad, but not an iPhone, you'll be able to download the app, but upon opening it, you'll be redirected to a version of the NHS website.

The reason older smartphones are excluded from the app rollout is that the app requires the Exposure Notifications framework developed by Apple and Google, which is only available in these latest versions. If you do not have a compatible smartphone, the NHS Test and Trace service will be your primary means of contact tracing or obtaining a COVID test.

In a joint statement, Apple and Google said they built the Exposure Notifications system to "enable public health authorities in their efforts to develop apps to help reduce the spread of the virus while ensuring people can trust in the privacy-preserving design."

In a BBC Breakfast interview, UK health secretary Matt Hancock was questioned about the fact that users with older smartphones won't be able to download the app. "Only a very small proportion of people have phones that don't have the latest iOS software," Hancock responded without giving any data to support this. "Of course there are technical requirements, in the same way that if you don't have a phone obviously you can't download it, but the vast majority of people have got the latest version of the Apple software." He added, "The best thing that they could do if they want to get the app, of course, is to upgrade."

"What, buy a new phone?" responded BBC breakfast presenter Charlie Stayt. He then added, "In terms of reaching those most at risk, for example, you said it yourself, those who have the least money are the least likely to have newer phones and equally well, and I'm wary of making sweeping generalisations here, but there is every chance that older people will have less sophisticated phones, maybe don't have smartphones at all. Surely those are some of the people you would most like to reach."

Hancock said the app is designed to work as part of "whole suite" of strategies and tools aimed at containing the spread of the virus.

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Concerns over access to the app are shared elsewhere, however. Attila Tomaschek, digital privacy expert at ProPrivacy, said in a comment that the app is "potentially cutting out a large percentage of would-be users, including the particularly vulnerable older generation, as well as those on low-incomes."

For those downloading the app, there are a few things you need to know. First of all, if you're worried about data usage, the UK's major network operators including Vodafone, Three, EE and O2, Sky and Virgin have confirmed that in-app activity will not come out of your data allowance.

Worried about battery drain? The contact tracing feature uses "low-energy Bluetooth" to log the amount of time you spend near other app users in addition to the physical distance between you. It will alert you if someone you've been close to tests positive for COVID-19 — even if you don't know them. If you're notified that you've been in contact with a confirmed COVID case, the app will advise you to self-isolate.

On the matter of privacy, Tomaschek also raised concerns about the app's use of QR codes and possible privacy implications. With the rollout of the app, businesses in England and Wales are now required by law to display the official NHS QR code posters from today.

"One must consider the very real privacy implications present here when an app uses QR codes to record users’ check-ins at various public spaces," said Tomaschek. "Not only can QR code check-ins paint an intricately detailed picture of a user’s location history (precisely what proximity tracking via Bluetooth is designed to prevent), but it can also be an extremely attractive attack vector for scammers to exploit." Tomaschek said that fake QR codes could be posted by scammers, and a malicious QR code could lead users to a site designed to infect users' devices with malware.

QR codes aside, the app generates a random ID for each individual's device and these random IDs regenerate frequently "to add an extra layer of security and preserve anonymity," according to a press release from the Department of Health and Social Care.

The app doesn't hold personal data like name, address, date of birth, and only asks for the first half of your postcode. No personal data is shared with the government or NHS.