==== DENM (Decentralized Environmental Notification Message) ====
DENMs are **event-driven** warning messages (ETSI EN 302 637-3). While [[en:c-its:messages:cam|CAMs]] are broadcast continuously, a DENM is only transmitted when something exceptional happens, and it is repeated for as long as the event is valid.

Typical triggers:
  - roadworks (including mobile roadworks / safety trailers)
  - stationary or broken-down vehicle
  - traffic jam ahead
  - emergency vehicle approaching
  - adverse weather or slippery road

A DENM contains, among other things:
  - the event type (a standardized "cause code")
  - the position and the area affected by the event
  - detection and validity times

On motorways, DENMs are typically sent by [[en:c-its:rsu|RSUs]] and roadworks safety trailers; vehicles generate them e.g. for emergency braking or breakdown warnings.