After reviewing many devices and algorithms which might be suitable to analyse changes in heart rate during practicing meditation, and studying the long-term effect 24 * 7, we found that the Firstbeat Body Guard

might be the most suitable device for this purpose.

The Firstbead Body Guard accuracy has already been tested against standard clinical ECG derived RRI during rest and different types of physical activity (walking, running, biking) in 19 healthy volunteers (2013):

https://assets.firstbeat.com/firstbeat/uploads/2015/10/white_paper_bodyguard2_final.pdf

and has 67 citations in other scientific papers according to Google Scolar since then.

The Bodyguard data can be uploaded to a computer with Firstbeat Bodyguard3 Exporter software (iOS, Windows), which is available free of charge. The Exporter software provides access to raw data files for ECG, RR-I and ACC in CSV format.

Heart rate from ecg raw data can be calculated in Python:

https://python-heart-rate-analysis-toolkit.readthedocs.io/en/latest/

R-R peak data can be used to calculate respiratory rate.