> For the complete documentation index, see [llms.txt](https://docs.tryterra.co/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tryterra.co/faq/help-topics/data-api-sdk/data-model-fields-and-units/rr-interval-and-streaming-coverage.md).

# What is RR\_INTERVAL and which devices stream speed?

`RR_INTERVAL` is the time between two consecutive R-waves (R-peaks of consecutive QRS complexes), typically provided by chest and arm straps alongside heart rate.

For real-time streaming:

* Generic BLE devices mainly broadcast heart rate (plus RR intervals when the device permits).
* Speed, distance, and calories during workouts are only streamed from **Apple Watch and WearOS** smartwatches.