Product Name: Button-Press Intercom SystemModel Number: LB-20LPlace of Origin: ChinaFunctions and features: 1) Both master station and substation can initiate calls and talks. Master station can listen-in/monitor substations 2) Master station can simultaneously talk, group-talk or listen-in (monitor) all groups of 20 substations 3) Master stations have alarm signal output to horns and strobe lights 4) With non-polarized N + 1 wires between master stations and substations