The GSC3516 is a SIP/Multicast Talk-Back Speaker that allows offices, schools, hospitals, apartments and more to build powerful voice intercom solutions that expand security and communication. The GSC3500 Series allows offices, schools, hospitals, apartments and more to build powerful voice intercom solutions that expand security and communication. These devices offer 1 and 2-way voice functionality with HD speakers and multi-directional microphones with a 4.2 meter voice pickup distance. The GSC3500 Series supports a wide-range of peripherals including Bluetooth devices, offers built-in whitelists, blacklists and greylists to easily block unwanted calls, provides integrated dual-band Wi-Fi and includes advanced acoustic echo cancellation. By pairing the GSC device with other Grandstream products, such as our desktop and cordless IP phones, IP PBXs, Wi-Fi APs and facility access systems, users can easily build a customized communication and security solution. Thanks to its modern industrial design and rich features, the GSC3500 Series are the ideal intercom speaker/microphone and paging devices for any indoor environment.