The WetronomeThe Wetronome is a water-proof metronome for swimmers and runners, designed to aid in 'stroke rate training.' (Yeah, I see. Let's just keep moving.) Although it looks simple at first glance, the Wetronome is designed to overcome issues specific to the environment it works in by remaining completely sealed. Programming the unit is done by waving a magnetic wand over the device, which will flash an internal LED in response. It's small enough to be worn under a swim cap or on goggles, and the power draw is so low that the batteries should continue to work for years worth of training. (Thanks, Mike!)

Product Page [Wetronome]