When trying the steps we’ve listed here, make sure that you’re very careful when putting objects into your headphone jack, SIM card reader, or lightning port. If you aren’t, you could potentially void your Apple warranty.
The size and shape of an iPhone’s LCI varies from model to model, but it’s usually pretty to tell if the LCI has been “tripped”, as we used to say at the Genius Bar. Look for a small line or dot just inside the edge of the SIM card slot, at the bottom of the headphone ...