I am assuming this is a fairly common feature for headphones? If so you might be able to switch models to one that has an off mode, if yours don’t.
IEM seal the ear canal causing a build up of moisture and ear wax that can lead to infection in some people.
That said, like with most IEMs, sleeves should be replaced sometimes (probably once a month or if you get any dirt on them—be careful with handling and don’t let that stuff get into your ear canal), so that should be factored in the price.
Which sleeves you choose makes a big difference—they are more or less the noise isolation part of IEMs, and they make or break your comfort when wearing. I swear by the combination of SE215 + Shure’s original black foam sleeves (or, if those cannot be obtained, Westone’s foam eartips). Passive noise isolation in this setup is better than ANC in AirPods Pro for me subjectively (although according to rtings.com’s measurements they go head to head), and is easy to wear for long periods of time.
(I guess I’m replying to thepostoffice but for the most part this is addressed to dghughes’s upstream post.)
I'm aware of how noise cancelling technology works it's by creating an opposing sound wave of equivalent energy to nullify the unwanted sound wave.
My theory is when I am off a call and I have the headset on my head with ANC enabled it's working to cancel the background noise. It's only needed on a call but it's obviously on all the time. These are not cheap headphones I've seen them for $300 so not cheap but I'm sure not the highest end.
I've tried taking them off, put around my neck, on my head between calls. But a few times I've fumbled them and hung up on someone or picked up before I was ready. My solution was to turn off ANC which made the sound clearer and my ears don't ring as bad as with ANC on.
My own anecdotal evidence but there is an obvious effect on my ears. I was about to go to the doctor the ringing was getting so bad.