Contact tracing apps may not be reliable, research finds

Trinity study finds problems with bluetooth technology, particularly on public transport

The bluetooth technology being used by contact tracing apps may be less accurate than initially thought, particularly on public transport, according to new research.

A new study from researchers at Trinity College Dublin looked at the use of contact tracing apps on public transport and also examined the Google and Apple exposure notification API (application programming interface) on which the apps are based.

The HSE's contact tracing app, expected to be released in the near future, uses Google and Apple technology, as do the apps created for Switzerland, Italy and Germany.

"We carried out an independent 'due diligence' analysis of the Google-Apple API on Android handsets. This API will be used in the Irish contact tracing app, and is already being used by the Swiss, Italian and German apps," said Prof Doug Leith, from the school of computer science and statistics at Trinity.


“We found that the way the API measures Bluetooth LE signal strength, probably to save on battery power, can make it much more inaccurate at estimating proximity.”

Trinity's Dr Stephen Farrell said there could also be issues with the technology on buses, for example.

“We found that the radio environment inside a bus is highly complicated, presumably due to all the metal which reflects the radio waves,” said Dr Farrell. “As a result, the signal strength can be higher between phones that are far apart than phones close together, making reliable proximity detection based on signal strength hard or perhaps even impossible.”

Prof Leith and Dr Farrell are working with the HSE and Department of Health testing both the technologies and the Irish app, which was developed by Waterford-based Nearform.

Prof Leith said updates to the API were pushed out silently to handsets by Google, without notifying users or giving them the chance to opt out. "This includes updates that can significantly affect contact tracing performance and, in turn, public health," he said. "This raises obvious concerns regarding oversight, and highlights the need for the governance of changes made by Google-Apple when it will eventually be deployed in Ireland. "

UK U-turn

Meanwhile, Britain said it would switch to the Apple and Google model for its Covid-19 test-and-trace app, ditching an attempt to develop an app by itself after the homegrown system did not work well enough on Apple’s iPhone, the government said on Thursday.

A smartphone app developed by the National Health Service (NHS) was initially expected to be rolled out nationwide in May but did not materialise. Health minister Matt Hancock appeared to blame Apple in part for the pivot, adding that the decentralised Google-Apple system would benefit from work done on the abortive NHS app.

“As it stands, our app won’t work because Apple won’t change their system, but it can measure distance. And their app can’t measure distance well enough, to a standard we are satisfied with,” he said at the daily news conference. “So we’ve agreed to join forces with Google and Apple, to bring the best bits of both systems together.”

Dido Harding, head of the test-and-trace programme, has described the app as the “cherry on the cake” of the overall test-and-trace system, playing down its centrality to the programme.

Officials running the programme admitted that the change of tack on the app was unplanned but denied that it was a setback, emphasising that they did not want to rush out an app which fell short of standards.

But the opposition Labour party said that warnings about the homegrown app had not been heeded. "This is unsurprising and yet another example of where the government's response has been slow and badly managed. It's meant precious time and money wasted," Labour health spokesman Jon Ashworth said. – Additional reporting: Reuters

Ciara O'Brien

Ciara O'Brien

Ciara O'Brien is an Irish Times business and technology journalist