One of the mysteries of COVID-19 is why oxygen levels in the blood can drop to dangerously low levels without the patient noticing.
It is known as "silent hypoxia" and as a result, patients have been arriving in hospital in far worse health than they realised and, in some cases, too late to treat effectively.
But a potentially life-saving solution, in the form of a pulse oximeter, allows patients to monitor their oxygen levels at home, and costs about £20.
They are being rolled out for high-risk Covid patients in the UK, and the doctor leading the scheme thinks everyone should consider buying one.
A normal oxygen level in the blood is between 95% and 100%.
"With Covid, we were admitting patients with oxygen levels in the 70s or low-or-middle 80s," said Dr Matt Inada-Kim, a consultant in acute medicine at Hampshire Hospitals.
He told BBC Radio 4's Inside Health: "It was a really curious and scary presentation and really made us rethink what we were doing."
Source: BBC News, 21 January 2021
See hub resource on the 'Covid Oximetry @home' project