CEL-FI PRO LTE/4G/3G Signal Booster &ndash; AT&T Boosts AT&T 4G LTE, VoLTE, 3G, and voice signal As long as you have 1 bar of AT&T signal at the window, Cel-Fi can boost your signal! Covers up to 13,000 square feet Cel-Fi is the ONLY signal booster authorized for use on the AT&T network and approved by the FCC for 100dB gain - providing a LARGER coverage area and 1000x greater gain than current analog boosters Network-Safe software prevents uplink system gain from exceeding path loss between Network Unit and closest tower, thus eliminating unnecessary rise in base station noise level.