# EN 50136 explained: grades and categories

Alarm signalling is specified in language that is easy to mix up. A system grade, a transmission category and the number of paths are three different things, and getting them straight is the difference between a compliant specification and a guess.

14 February 2026

[Alarm Signalling](https://netavo.com/insights)

## Three different measures

The first measure is the alarm system grade, which describes how resistant the whole alarm system is to defeat, and is set by the risk at the premises. The second is the alarm transmission category, defined by EN 50136, which describes how the signal gets from the premises to the receiving centre and how quickly a failure of that path is detected and reported. The third is simply how many physical paths carry the signal, single-path or dual-path.

These are related but not interchangeable. A higher system grade tends to call for a more demanding transmission category, and a more demanding category often needs more than one path, but the number of paths on its own establishes neither the category nor compliance. A specification that says only “dual path” has not yet said what it needs to say.

## Letting the requirement set the category

The right order is to establish the premises' risk and system grade, let that determine the transmission category required, and only then choose a signalling product that meets it. The insurer, the alarm receiving centre and the relevant scheme all have a stake in that decision, so the useful questions are for them: what grade is required, what transmission category that implies, and what evidence of performance the product must provide. BS EN 50136 defines the transmission categories, and PD 6669 provides UK-specific supporting guidance.

Netavo provides alarm signalling with up to four verified paths per site, which supports demanding transmission requirements. The signalling supports up to DP4, the most demanding dual-path category, and is compliant with EN 54-21, EN 50136-1, -2 and -3 and EN 50131. The category a particular site needs is still set by its grade and risk.

## Common questions

### Is a grade the same as a transmission category?

No. The grade describes the alarm system's resistance to defeat and comes from the premises risk. The transmission category, from EN 50136, describes how the signal is carried and how fast a path failure is detected. One informs the other, but they are different measures.

### Does dual-path signalling guarantee compliance?

No. The number of paths alone establishes neither the transmission category nor compliance. The required category comes from the system grade and the risk, and the product must be shown to meet it.

### Who decides the required category?

It follows from the premises risk and grade, agreed with the insurer, the alarm receiving centre and the relevant scheme. Establish the requirement first, then choose a signalling product that meets it.

## Related services

### [Alarm Signalling & Critical Paths](https://netavo.com/services/signalling)

Resilient multi-path signalling for fire and intruder alarms, continuously monitored.

### [Fire & Security](https://netavo.com/sectors/fire-and-security)

Signal Dynamic alarm signalling over up to four verified paths, for installers and alarm receiving centres.

## Specifying alarm signalling?

Tell us the grade and transmission requirement for the premises, and an engineer will talk through a signalling path that meets it.

[Work with us](https://netavo.com/work-with-us)

Source: https://netavo.com/insights/en-50136-explained