Proxximos founders co-led a project in early 2020 to trial digital contact tracing on the Isle of Wight, alongside other aspects of the UK Test and Trace system.  The results of this trial were studied by Oxford University and published by The Lancet.  The study showed that the approach effectively eradicated Covid-19 on the Isle of Wight during May 2020.  The R-rate in the Isle of Wight was the 3rd highest in all of the UK at the beginning of May, but by the end it was the 12th lowest.  Sadly, NHS Test & Trace had decided to use a different approach by the time this study was published, which generated a “pingdemic” in the UK, but made little difference to the course of the epidemic.  Here is the paper Epidemiological changes on the Isle of Wight after the launch of the NHS Test and Trace programme: a preliminary analysis – The Lancet Digital Health