Although this was posted some time ago, I'll answer it for information purposes for anyone else wondering the same.

I've had a few holter monitors over the years. Ever since my episode of Atrial Fibrillation in 2017, my GP sticks a monitor on me at the mention of any (possible) cardiac symptoms.

Bathing with it on really depends on what type of device you're wearing.

Older devices: The first device I wore must have been around from when holter monitors were invented. It was the size of a mobile phone. I had to bathe with it dangled over the bath.

Newer device: The device my GP gave me was so cool. It was tiny it fitted around my neck on a little plastic chain, and I Was able to bathe with it on.

NOTE: I said bathe, not shower. Showering with these devices is NOT recommended.

And yes, they attach to your chest only AFAIK.

Good luck