But the sensor is disposable and needs to be replaced when the battery wears out. In future versions, batteries could be avoided all together, says Berkeley's Huggins, since researchers have shown that power-harvesting circuits that store energy from vibrations can be used instead of batteries in some sensor applications, and the environment of a running shoe could be ideal for such technology. If this modification were made, it could give the sensor "an extended or infinite life," he says.

To Huggins, the kit is exciting because it's a "clever and cute" application for wireless sensors, and opens up opportunities for added features and new applications. For instance, he says, if the sensor used a more complicated accelerometer -- one that could measure acceleration in multiple directions -- it would be possible to calculate calories burned on inclines and stairs. Also, it could calculate the shock experienced when a foot hits the ground. As shoes wear out and shock increases, you could be reminded that it's time to buy new shoes.

What's more, adding GPS capability to the system could let people map their jogging routes. This improvement, Huggins says, could be done easily and inexpensively. Rather than installing a GPS receiver into the sensor, it could be "part of the higher valued iPod, which could re-use the GPS for other location-based services," he says. While out for a morning jog, your iPod could help find a coffee shop or a bus route, if you get tired.

Real-time biometric data could also be integrated with such a sensing device. Pulse, temperature, glucose, and lactate levels could be monitored with an array of microneedles, says Huggins. And it wouldn't have to be messy or painful, he says, because microneedles can be as short as 150 micrometers. At that size, Huggins says, the needles would penetrate the skin without touching nerves or blood vessels.