This European Standard specifies the requirements for the performance, reliability and security characteristics of alarm transmission systems. It specifies the requirements for alarm transmission systems providing alarm transmission between an alarm system at a supervised premises and annunciation equipment at an alarm receiving centre. This European Standard applies to transmission systems for all types of alarm messages such as fire, intrusion, access control, social alarm, etc. Different types of alarm systems 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 in the context of this standard. The term alarm is used in this broad sense throughout the document. Additional alarm transmission requirements of specific types of alarm systems are given in the relevant European Standards.