A bra or pants rigged to monitor heartbeat or blood pressure could dial 999 at the first sign of a problem, say Dutch researchers.
The device can measure heart rate
The "biomedical" underwear has been designed by electronics giant Philips, and can currently monitor the heartbeat of the wearer.
If it spots signs of heart trouble, it uses wireless technology to summon the emergency services.
However, it could be some years before the technology is in the shops.
The bra, belt or briefs each have electrodes built into their fabric, and use the thread in the fabric to send data to a small microprocessor.
This analyses the signals, and has been taught to discriminate between dangerous changes in heart rhythm.
Koen Joosse, from Philips Research, said that the device would be able to work out whether the wearer was taking exercise and discount high heart rates generated by physical exertion.
Wearable computers have not always been the height of fashion
He told BBC News Online: "What we have ended up with is convenient for people to use in an unobtrusive way.
"What we have to do now is test it on a larger number of people, and perhaps seek for it to be approved in Europe.
"There are a lot of companies taking this direction as people become more interested in preventive medicine."
He said that he hoped that such a device would not simply be useful to give to patients with existing heart problems, but would eventually be used by a wider public.
He said he expected other measurements, such as blood pressure could also be taken by the clothing.
And he promised that the hi-tech underwear would be as convenient as normal clothing.
"It can be put through the washing machine - and ironed if necessary."