I’ve used the A9 on my belly and felt some movement. I don’t observe the same thing with M1. Bob and his wife said it could be that the battery is weaker on the M1.
I tried using my HRV monitor at the same time as the ICES on the belly - no difference. Is there a specific location you tried?
Many of my friends felt movement with the ICES but it’s unpleasant.
A few times I got ear acupuncture and my HRV shot up by 20 points (my baseline is around 50). It’s super relaxing, so I think that’s what I would expect from a vagus nerve activation.