The Eartec UltraLITE 4-Person Headset System is a professional full duplex intercom for up to four people. One "master" sets the digital sequence and your crew can enjoy simultaneous wireless communication within a quarter mile range. The rechargeable batteries fit neatly into the earcups and run for approximately 6 hours. A multi-bay charger is included and will charge batteries fully in about 3 hours. These fully-adjustable noise cancelling microphones are effective for communication on busy sets and during events. Please note that these are intended for use in the the United States only. Also note that this set is a stand-alone set and cannot be daisy-chained with other sets.