Critical Communications headsets is a full duplex headset-to-headset Bluetooth system. Typically sold in a pair with one “Master” and one “Slave” headset gives you full VOX communication with a range up to 1000ft. Expansion headsets can be added to increase the number of people talking on the system, you can add up to 3 expansion headsets for a total of 5 people communicating. These headsets daisy chain to allow further range, meaning if each person is 1000ft apart they have 5000ft of total range from first person to last person.