At festivals all over the UK this summer, Vodafone has been trialling the new 'Power Pocket'. Built into either a 'Recharge' sleeping bag or a pair of 'Power' denim shorts, the device draws on body heat to charge mobile phones. Vodafone developed the Power Pocket in conjunction with the University of Southampton's Department of Electronics and Computer Science. 'We've been working on printed smart material since the late 1980s,' Professor Stephen Beeby explains on the company's blog. 'But that was high-temperature stuff designed to be used on ceramics. We got into the topic of energy harvesting in the late 1990s, and we brought the two together to make smart materials for harvesting energy. We started on thermoelectric materials in 2003, but our printed thermoelectric material work has only been the last few years.' The smart material is made up of 'thermocouples', a whole bunch of which form a 'thermoelectric module'. One side of this is cold and the other is hot. The introduction of heat creates both a voltage and a current, which, in unison, give rise to electric power. In other words, the warmth generated by sleeping or dancing contrasts with the external cold air. Technically, this reaction is known as the 'Seebeck Effect'. At the moment, eight hours' time in the sleeping bag produces enough energy for 24 minutes of talking and 11 hours on stand-by, while a day's worth of activity in the shorts provides four hours of smartphone charge. [via Inhabitat]