Nextivity Cel-fi DUO 3G/4G/LTE Cell Phone Signal Booster - for T-Mobile Cellular Service Reduce Dropped Calls and Dead Zones. All you NEED is 1 BAR TO GET 5!! Can only be used in locations that already receive (weak) cellular signals. This unit cannot boost a non-existent signal. Easy to Install-True Plug and Play, Self-Configuring, No external Antennae or Cabling needed. Professional installation Not required! Cel-Fi is the ONLY Cellular Signal Booster Authorized for use on the T-Mobile Network and Approved by the FCC for 100dB Gain-Providing a LARGER Coverage Area and 1000 Times Greater Gain than current analog boosters The Cel-Fi All Digital Booster can Cover up to 13,000 sq. ft., making it IDEAL for Homes and Offices and Each Cel-Fi system can SUPPORT up to 60 Concurrent Users All Digital Simultaneous Voice and Data 3G/4G/LTE (T-Mobile Dual Band MHz 1700,1900). Only compatible with T-mobile cellular service. Will not work with Sprint, AT&T, nor Verizon.