The Shimano Di2 EW-WU111 Inline Wireless Unit boosts the system's ease of use by adding Bluetooth connectivity in addition to carrying over ANT to pair with an even wider range of devices. Paired with Shimano's E-Tube Project Wireless app, the Inline Wireless Unit lets you customize your drivetrain and update firmware right from your smartphone or other Bluetooth equipped device.This diminutive component is like a black box for your bike, feeding data from your derailleurs to your phone or tablet so you can monitor drivetrain metrics like gearing and battery life. The latter is especially useful, as it's looking to be the most effective way the industry has come up with to ensure you won't unexpectedly run out of juice during the trip home. It also measures general riding metrics, so you're not sacrificing the functionality of a normal computer by adding drivetrain info to your cockpit. Your pedal revolutions will also be televised.The Di2 EW-WUlll Inline Wireless Unit is compatible with Shimano's E-tube Di2 systems. In addition to it Bluetooth connectivity, it transmits via ANT to Shimano's own PRO computer, as well as other ANT equipped head units.