Japan's top mobile phone operator NTT DoCoMo is to unveil a smartphone with changeable "jackets" that measure bad breath, body fat and even radiation levels.

DoCoMo says it has developed technology that allows users to measure their own bodies or surroundings by slipping their smartphones inside sensor-embedded shells.

The company will showcase the technology at the Combined Exhibition of Advanced Technologies, a fair featuring the latest in high-end gadgetry, starting in early October near Tokyo.

"Many customers have been nervous about radiation since the Great East Japan Earthquake," DoCoMo spokesman Daisuke Sakuma told AFP, referring to the 9.0-magnitude quake and tsunami of March 11 that sparked a nuclear crisis at the Fukushima atomic plant.

"We had been thinking what services we can provide to address these customer needs as a telecom carrier."

The tsunami knocked out cooling systems at Fukushima Daiichi, sparking meltdowns that sent radioactive materials into the air, soil and sea.

Worries over the health implications of the leak, which is still not plugged, have sent demand for radiation-measuring devices soaring in Japan.

DoCoMo will show off three kinds of "jacket" for use with a model of smartphone loaded with the appropriate software.

As well as radiation, the company said it would also demonstrate a case that determines if the holder has bad breath or smells of alcohol as well as checking levels of skin-damaging ultraviolet light.

A third case, dubbed the "health management" jacket, will measure body fat and muscle bulk.