If you are wearing a suit, a smartphone makes the trouser pockets bulge a lot, so it's common to keep it in your shirt pocket or jacket inside pocket - Both of which is next to your heart.
The FDA [1] advises "don’t carry the phone in a shirt or jacket pocket directly over the pacemaker." as well as the American Heart Association [2] "Avoid keeping your cell phone in your front chest pocket."
One hopes people with a device keeping them alive would have an incentive to follow instructions, especially if it doesn't involve addictive substances. They also get told to avoid metal detectors, and they know to do this, so it's probably, hopefully, an easy habit to change
