This standard specifies the requirements for the performance, reliability and security characteristics of alarm transmission systems. It covers the general requirements for connections providing signalling between an alarm system at a supervised premises and annunciation equipment at an alarm receiving centre. EN 50136-1 Applies to transmission systems for all types of alarm messages such as fire, intrusion, access control, social alarm, etc. Different types of alarm system may in addition to alarm messages also send other types of messages, e.g. fault messages and status messages. These messages are also considered to be alarm messages. The term alarm is used in this broad sense throughout the document. Additional requirements for the connection of specific types of alarm systems are given in the relevant European Standards.