Have you ever had one of those days when you had to make an emergency phone call with your mobile phone and couldn’t because you ran out of power? There is a device that now allows people to charge their mobile phones with the use of their own body and a bracelet. The bracelet is called a Dyson Energy Bracelet. The gadget works and uses the Thermoelectric Effect.
The Thermoelectric Effect is the direct conversion of temperature differences to electric voltage and vice versa. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when a voltage is applied to it, it creates a temperature difference (known as the Peltier effect). At an atomic scale (specifically, charge carriers), an applied temperature gradient causes charged carriers in the material, whether they are electrons or electron holes, to diffuse from the hot side to the cold side, similarly to a classical gas that expands when heated; hence, the thermally-induced current.
This effect can be used to generate electricity, to measure temperature, to cool objects, or to heat them or cook them. Because the direction of heating and cooling is determined by the sign of the applied voltage, thermoelectric devices make very convenient temperature controllers.
Of course, the gadget won’t be able to fully charge your cellphone, but it can charge it enough to at least allow you to have a minute or two of talk time.