Joggers using the iPod Sport kit to keep fit are putting their personal privacy at risk, warn scientists.
The academics showed how easy it was to track those using the combination of music player and running shoe sensor.
In the worst scenario suggested by the scientists, stalkers could use the tracking data to "engineer" encounters with victims.
The researchers said gadget makers should do more to protect privacy and stop hardware being abused in this way.
The Nike iPod Sport kit uses radio to link a sensor in a runner"s shoe to another gadget that clips on to an iPod Nano.