Conventional heart rate monitors fall down in two areas when swimming: firstly the chest strap isn't always compatible with those long reaching pulls; secondly, looking at the display while swimming can really put you off your stroke.
FINIS think they have a solution in their AquaPulse. If there wasn't a picture to go with this, you'd hardly believe it. The AquaPulse attaches to a goggle strap with a sensor that clips onto your earlobe to detect your heart rate.
Using the same bone conduction technology that they put into their MP3 players for using in the water, the sound is then transmitted through the skull so you can get updates on your heart rate - with intervals of your choice from 20 seconds up to 5 minutes.
No information on whether you can set upper or lower limits so it only tells you when you are out of your training zone, as this would seem a good option for feedback.
Apparently you can get 8 hours from the battery too, so it won't quite get you across the channel.
Likely to be snapped up by triathletes everywhere (you know you love this stuff), the AquaPulse will be available from May, costing $139.99.