If you’re a triathlete, you might be interested in buying a run speed and distance device that you can also use on the bike-and perhaps even in the pool. Such models do exist.
Polar’s high-end “multisport computer” is a GPS-based speed and distance device with integrated heart rate monitor that can also be linked up with power sensors, allowing you to truly do it all with a single device. Some Garmin and Timex speed and distance devices can be mounted on a bike handlebar and used as a cycling computer. Suunto sells packages for triathletes as well. Along with a heart rate monitor strap and foot pod they include a pedaling cadence sensor and a spoke-mounted sensor that delivers bike speed and distance data to the display watch, which is worn during both cycling and running. This setup allows you to easily capture data for a complete “brick” workout or triathlon event.
The best possible way to pick a speed and distance device would be to wear-test all of them and go with your favorite. That’s not a realistic possibility, so the best alternative is to wear-test by proxy-in other words, to gather reviews from the owners of the various devices. Google a phrase such as “Garmin Forerunner reviews” and you will be led to product evaluations from commercial websites, bloggers and others. This research should help lead you to the device that is most ideal for your needs.