I have, many years ago with a bespoke 3rd party product (mildly succesfull but issues) and more recently from an RT product which I think is available from RT direct.
This is using the RT product
https://www.youtube.com/watch?v=rkfYNWcPlSI
It's simply a receiver/processing unit which plugs into the serial port of the DL1 and connects to a regular chest strap. It worked really well.
I found the knowledge base article on it but can't find a product listing for it.
https://www.race-technology.com/wiki/in ... ateMonitor