There are times when its impractical - for various reasons - to cut a 3" to 4" hole through an isolation barrier. But your employees and your customers still have a way to communicate - clearly, and calmly. In such cases, the Alpha Communications/Norcon TTU-3 is the communication system of choice. The prismshaped units of the TTU-3 are ideal for mounting on a countertop on both sides of a barrier. Yet they allow free communication through barriers typically found in banks, cashier's booths, information booths, and similar environments.