Ant power.

The Wahoo Fitness Fisica Sensor Key for iPhone is a simple solution to connect your iPhone to all of your ANT+ exercise sensors and ANT+ GPS devices. It wirelessly pulls data from ANT+ heart rate monitors, cadence sensors, and GPS devices, integrating exercise-savvy metrics with powerful iPhone applications for real-time analysis. It's compatible with a wide variety of apps, such as Wahoo Fitness, Runmeter GPS Pedometer, Cyclemeter GPS, and Map My Fitness.

It doesn't run on a battery, so you won't need to worry about charging it up before working out. Additionally, it transmits a signal up to 10 feet, allowing you to stash it in a pack, wear it on an armband, or stick it in your pocket.

• A dongle for linking iPhones with cycling devices
• Adds ANT+ compatibility to your smartphone
• Transmits up to 10 feet