The Garmin Forerunner 305 GPS unit with heart rate monitor. You can keep tabs on how hard you're working, making sure to neither over or under exert yourself. (Photo by Walter Cruz/Dallas
Amazon.com: Garmin Forerunner 305 GPS Receiver With Heart Rate Monitor (Discontinued by Manufacturer) : Garmin: Electronics
Garmin Forerunner 305 Wrist-Worn GPS Personal Training Device with Heart Rate Monitor (discontinued by manufacturer) (discountinued by manufacturer) : Amazon.co.uk: Sports & Outdoors