Cel-Fi DUO improve 3G/4G/LTE cellular service by eliminating dead zones and dropped calls. With up to 100dB of gain, it will improve cellular service and reduce your cell phone’s power requirements to extend its battery life. The Cel-Fi DUO cover up to 1,500 square meters of indoor space per system. It’s fully self contained and self-configuring, requiring no external antennas or wiring required. Simply plug it in to boost indoor cellular coverage. Band 1/3.