Can someone track you using (IMEI, GPS, IP Address, etc…) if your iPhone is offline and doesn’t have a sim card?
If it’s off? No.
If it’s on but no SIM card? Depends. In theory no, but a lot of phones can still make emergency calls if they don’t have a SIM, which means they can ping towers, which means they can (in theory) be tracked. How this would work, or even if it happens, I have no idea. If you don’t have a SIM but you have apps installed (maybe via WiFi) then you’re subject to the usual concerns there, and often they can tie their activity to the phone, if not necessarily you personally (although if the phone is at your house every night at 3am, it’s reasonably easy to guess if a human wants to know).
More important question - does it matter? Does your threat model require this level of paranoia? How does it measurably impact your life if a phone company can track your location? If it does sometimes - like you’re going to a potentially worrying political meeting, or social meetup, or just makes you feel icky - then leave your phone behind. You usually don’t need it anyway. And if you must take it, just turn it off before you leave, or as soon as practical.
According to Edward Snowden, your phone is always talking even when powered off. I’ll see if I can find the quote. (I think he was assuming that you have a sim in.)
I bet that dystopia law enforcement can still find you. Hense, faraday bags if your threat model calls for it.
Yeah… “off” is a relative term. iPhones have a “find my” function that works even when “powered off”. Phones have at least two subsystems in them: the smartphone part that you normally interact with and the base band radio system, often made by Qualcomm (not Apple or Google or Samsung). That system could be doing it’s own thing entirely.
Well. That’s unsettling.