This Shimano Di2 Bluetooth frame or bar plug mount allows you to charge and check the battery level of your Shimano Di2 electronic shifting system. Thanks to its Bluetooth-compatible design (Bluetooth module available separately), you can easily connect to your Shimano Di2 to change shift modes such as manual shift, synchronized shift 1 and synchronized shift 2. Its built-in LED lights will illuminate to indicate the mode you have selected by a green or red light system. If your bike receives a strong impact, the rear derailleur (RD) protection function kicks in and the connection between your motor and the link is momentarily severed so that the rear derailleur will no longer operate. This is done in order to protect the system at times such as if the bike falls over. The Shimano Di2 junction box allows you to press the button on junction (A) to restore the connection between the motor and the link and to clear the RD Protection function for the rear derailleur. To top it off, this handy device features water-resistant connectors so you can keep your Di2 running in peak performance, whatever the weather conditions. Please note: You need the additional Bluetooth module Shimano SM-EWWU111 to enable Bluetooth. This Shimano SM-EWWU111 unit allows you to connect to a Bluetooth device once installed however, the EW-RS910 alone does not allow for this functionality and would work in tandem with the Shimano SM-EWWU111.