What is EN 50136, and what do ATS categories mean?

EN 50136 is the standard for alarm transmission systems — the signalling path between your alarm and the Alarm Receiving Centre. It classifies paths by how quickly a failure is detected and reported, which is why a monitored system notices a cut line or a lost mobile signal rather than simply going quiet.

Signalling is the part of a monitored system that an intruder attacks, so the standard is mostly about resilience and supervision. A supervised path is polled: if it stops answering, the ARC knows within a defined time and can treat the silence itself as an event.

Higher categories mean shorter detection times and more redundancy, typically achieved with dual-path signalling — for example broadband plus a mobile network — so that losing one path does not lose the connection.

The category you need follows from the system grade and, often, from your insurer's requirements. The question to ask an installer is not 'is it monitored' but 'what happens, and how fast, if this path fails' — and to get the answer in writing.