Why won't my Nike+ sensor work anymore?

I recently bought a new Nike+ sensor for my iPod touch, and was using it for about 2-3 days just fine and dandy. I haven't abused it or anything, it hasn't been subject to any hard wear at all, but it suddenly stopped working yesterday. My iPod touch simply won't detect movement with it anymore, at all. I've restarted/recharged my iPod and everything, but no dice. I've even walked a good mile or so without the sensor being detected at all. What might be wrong, and what could I do to fix it?