How quickly we walk offers significant clues about the state of our health, research suggests.
A slowing pace could be an early warning of heart failure, dementia or cardiac disease, according to Daily Mail.
Scientists at the Massachusetts Institute of Technology believe walking speed is nearly as important as pulse rate or blood pressure.
They have developed a sensor that hangs on the wall and transmits radio waves to detect a person's gait and stride length as they move about their home.
Experts think the WiGait device, which is roughly the size of a small flatscreen TV, can predict the onset of health problems through analysing the data it records.
The technology has been tested in care homes in the US and was able to measure walking speed with an accuracy of 95 to 99 per cent in the research phase.
The waves emit 100 times less radiation than a mobile phone and can pass through walls, so that each unit can monitor a radius of 30ft to 40ft - covering an area roughly the size of a small flat.
Chen-Yu Hsu, a PhD student and lead author of the research, said that the device would be inexpensive if mass-produced and could also be used to monitor speeds of healthy individuals.
They would be able to view their walking speeds on an app and also receive alerts if they are too sedentary - encouraging them to take more exercise.
Such data could be particularly useful for doctors and relatives who want to keep an eye on an elderly person, with emergency alerts sent in the event of sudden decline.
Professor Dina Katabi, an author on the study, said: "Many avoidable hospitalisations are related to issues like falls, congestive heart disease, or chronic obstructive pulmonary disease, which have all been shown to be correlated to gait speed."
The findings will be presented later this month at the ACM Conference on Human Factors in Computing Systems in Colorado.
They back up a 2011 University of Pittsburgh study that found faster walkers could expect to live up to ten years longer.