Connecting your eTrex with other devices

The eTrex 30 and 30x are able to connect to a variety of accessories. I actually use my Garmin Forerunner 45 to measure heart rate, which displays on the eTrex 30 without a problem. You can use cadence and speed sensors as well, there’s even a temperature sensor (Garmin Tempe) that will work as well

On this website you can look up which accessory works with the Garmin eTrex.