The device combines an antenna and sensor which can pick up respiratory and heart activity when connected to a mobile phone and placed in front of a patient.
The information could then be sent to a remote health monitoring centre using the existing telephone network.
It has been designed by researchers at Lucent Technologies' Bell Labs.
Remote care
The device works by monitoring the microwaves transmitted by a mobile.
Some of the microwaves bounce back to the phone from the chest, heart and lungs of the person using it.
The add-on module picks up these signals to produce a pattern of the user's heart beat and breathing.
It is estimated that 100 million Americans suffer from chronic health problems such as heart disease and lung disorders.
With the elderly population also rising, it is essential to develop applications to monitor health outside hospitals, both to save money and cut down on waiting times.
Healthcare via broadband
One of the researchers on the project Olga Boric-Lubecke said the wireless philosophy of "anywhere, anytime" can be usefully applied to the medical world.
She told the BBC programme Go Digital that patients would be less anxious using such a device as it would not require a trip to the doctor's surgery.
Telemedicine, the term given to the use of telecommunications for diagnosis, treatment and patient care, is set to become a multimillion dollar industry in the States.
In the UK Prime Minister Tony Blair has committed to connecting every GP surgery in the country to broadband by 2006.
This would enable remote diagnosis using video-conferencing.
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