For mobile phone users, a flat battery or a lost charger are among the frustrations of modern life.

Now new research promises a way to recharge phones using nothing but the power of the human voice. Electrical engineers have developed a new technique for turning sound into electricity, allowing a mobile to be powered up while its user holds a conversation. The technology would also be able to harness background noise and even music to charge a phone while it is not in use.

However, there could be a downside to the innovation, if it gives people a new reason to shout into their phones as they attempt to squeeze in every extra bit of power they can.

The technology uses tiny strands of zinc oxide sandwiched between two electrodes. A sound absorbing pad on top vibrates when sound waves hit it, causing the tiny zinc oxide wires to compress and release. This movement generates an electrical current that can then be used to charge a battery.

A prototype of the technology was able to convert sound of around 100 decibels - the equivalent of noisy traffic - to generate 50 millivolts of electricity.

This is not enough to charge a phone properly, but Dr Kim and his colleagues hope that by altering the material the wires are made from they will be able to produce more energy at lower sounds levels.

He said: "Our current output performance can be applied to various electronic devices with low-power consumption such as self-powered sensors and body-implantable tiny devices. We believe that we can realize more efficient sound-driven nanogenerators."

Researchers and some manufacturers have already started looking at using 'energy scavenging' as a way of powering portable electronic devices.

Scientists have developed devices that can use the heartbeat to power MP3 players, while Nokia has filed a patent for a device which harvests energy from movement, much like a kinetic energy powered watch.