Staff and athletes in Sunday's London Marathon must wear social-distancing technology around their necks.
The Bump device, which makes an audible alert when the wearer is too close to others, will be worn by the 100 elite competitors and 500 event coordinators.
The race, 19 laps of a closed course in St James's Park, screened from public view, is the first major marathon since the Covid-19 pandemic, organisers say.
Non-elite runners can participate in a 24-hour virtual version of the event.
The device will not be worn during the race, however, with athletes taking them off just before the starting line.
The Bump uses radio-frequency technology, allowing organisers to track when athletes and staff are within a defined distance of one another.
And if one tests positive for coronavirus in the subsequent two weeks, those who have been in close proximity will be notified.
The device was designed by robotics company Tharsus, based in Blyth, Northumberland.
"This weekend's event is the culmination of months of planning around how to deliver a socially distanced 2020 Virgin Money London Marathon that is safe for all participants and stakeholders," director Hugh Brasher said.
"This technology has played an important role, giving our athletes and internal teams extra confidence to engage with the event safely."