Just thumbing through the giant new Argos catalogue and I spotted this beauty:
Argos underwater timer For £20 the technology is stunning but I'm not sure the earpieces could be worn with a bike helmet - might be worth a go though as its a radio as well !!!!
There is also this amazing piece of kit as well but it sadly looks to big for bike use...
http://www.argos.co.uk/webapp/wcs/st...clickfrom=name