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According to the team from the University of Michigan, the chip - called the Phoenix Processor - also uses ten times less power in active mode than comparable chips. The Phoenix measures one square millimetre, which is the same size as its thin-film battery. The researchers also claim that the energy stored in a watch battery would theoretically be enough to run

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the Phoenix for 263 years.

"Low power consumption allows us to reduce battery size and thereby overall system size. Our system, including the battery, is projected to be 1,000 times smaller than the smallest known sensing system today," said David Blaauw, a professor in the department of electrical engineering and computer science. "It could allow for a host of new sensor applications."

To maintain such low power, the team focused on the chip's activity in sleep mode - its default mode - so that the chip 'wakes up' for a tenth of a second every ten minutes to compute a set of 2,000 instructions.

"We keep time to 10 minutes plus or minus a few tenths of a second. For the applications this is designed for, that's okay. You don't need absolute accuracy in a sensor. We've traded that for enormous power savings," explained Scott Hanson, a doctoral student at the university's department of electrical engineering and computer science.