27 50 00 Distributed Communications and Monitoring Systems
27 51 00 Distributed Audio-Video Communications Systems
27 51 13 Paging Systems 27 51 13.13 Overhead Paging Systems 27 51 16 Public Address Systems 27 51 19 Sound Masking Systems 27 51 23 Intercommunications and Program Systems 27 51 23.20 Commercial Intercommunications and Program Systems 27 51 23.30 Residential Intercommunications and Program Systems 27 51 23.50 Educational Intercommunications and Program Systems 27 51 23.63 Detention Intercommunications and Program Systems 27 51 23.70 Healthcare Intercommunications and Program Systems 27 51 26 Assistive Listening Systems 27 51 29 Emergency Communications Systems 27 51 29.13 Rescue Assistance Signal Systems 27 51 29.17 Two-way Radio Communication Enhancement Systems 27 51 33 Occupancy Indicator