27 51 00 Distributed Audio-Video Communications Systems
27 51 33 Occupancy Indicator
27 51 13Paging Systems27 51 13.13Overhead Paging Systems27 51 16Public Address Systems27 51 19Sound Masking Systems27 51 23Intercommunications and Program Systems27 51 23.20Commercial Intercommunications and Program Systems27 51 23.30Residential Intercommunications and Program Systems27 51 23.50Educational Intercommunications and Program Systems27 51 23.63Detention Intercommunications and Program Systems27 51 23.70Healthcare Intercommunications and Program Systems27 51 26Assistive Listening Systems27 51 29Emergency Communications Systems27 51 29.13Rescue Assistance Signal Systems27 51 29.17Two-way Radio Communication Enhancement Systems27 51 33Occupancy Indicator