A signal booster is an interchangeable term for cellular repeater, cell phone repeater, or wireless cellular signal booster, a type of bi-directional amplifier (BDA) as commonly named in the wireless telecommunications industry. It is a device used to boost the cell phone reception to the local are by using an antenna, a signal amplifier and an internal rebroadcast antenna. These are similar to the cellular broadcast towers used to broadcast by the network providers, but are much smaller, usually intended for use by one building. Modern cellular repeater amplifiers work by rebroadcasting cellular signals inside the building. These solutions generally use an external, directional antenna to capture the outside cellular signal, which is then transmitted to an amplifier unit which amplifies the signal, and retransmits it locally, providing significantly improved cellular and wireless coverage. The more advanced models often also allow multiple cellular signals to use the same repeater at the same time. Making solutions suitable for commercial and residential use.