Bluetooth 4.1 for connection with 4 helmets and 2 devices. FM radio with STD and HD earbuds. The SF4 is the perfect device for riding with friends by providing connectivity for small groups. The SF4's 4-way intercom has a range over 1.2 kilometers (.80 miles) so you can easily stay connected with your group in open terrain. The SF4 also uses smartphone connectivity, allowing for music streaming, taking and making phone calls, and hearing turn-by-turn GPS directions. Most importantly, riders can listen to music and use the intercom simultaneously, using the Audio Overlay™ feature. Plus, with the Quick Charging capabilities, you will be ready to start your ride in no time. Each SF4 comes with one standard and one HD speaker set. The HD speakers will take your ride to the next level with louder, clearer quality audio. The standard speakers are a bit smaller in size and may be a more comfortable choice for some riders. The SF4 is available in a standard package with 1 headset and a dual package with 2 headsets.