Spec Sheet Preview: Low-Profile Voice Communication System. Ideal for High Security Locations The TTU-4 Talk-Thru communication system is particularly suitable for low ambient noise environments that require an unobtrusive, yet tamper-resistant voice communication system. It features half-duplex (VOX) operation which allows both parties to talk and listen without using any pushbuttons or controls, for easy, natural conversation. The TTU-4's counter-mounted design eliminates the need for cutting into a barrier. It's low profile inst …