How to prevent someone from turning off a locked iPhone after it's lost?

Your phone is still locatable with Find My even when it is turned off. You will see that confirmation on your screen every time you slide to power off the phone. The premise in your original post that the thief can shut off your phone so you cannot locate it is simply not true. That message is seen here and it may be beneficial if it was powered off as your battery will last longer giving you more time to locate it.

MAriusMKM wrote:

IDK if someone thinked about this ! buttt...is a big big problem.

If will happen to lose your phone, the person who will find it can turn off the device even if is locked and you can't locate him anymore !!!

I agree with Kurtosis12. It is not a security problem. They can't get into the phone as long as you used a Passcode and enabled Find My on the phone, your data is safe. The vast majority or lost or stolen phones are never recovered. Thieves know to put them Faraday bags, which block them from broadcasting their location anyway. So powered on or powered off really won't make much difference.

MAriusMKM wrote:

Yes I agree that in the case of theft there are professional people who can influence its location, buuuttt in this case it's about loss. You loss it and someone random in the street finds him and stops him, simple and easy.

I'm not sure what you're hoping to accomplish here? You aren't speaking with anyone from Apple on this user to user only forum. You are speaking ONLY with other users like yourself and Apple doesn't read here for user feedback. Think about this however, even if there was some failsafe mechanism to prevent a phone from being powered off, its battery will eventually run down and the phone will power off anyway. I don't think you've really thought this through very much.

If you think Apple needs to consider something, feel free to use this link to share your thoughts with them --> Feedback - iPhone - Apple

You do realize that iPhone thieves are very fond of wrapping a stolen phone in aluminum foil, so the phone cannot send or receive a signal at all......correct?

Or, they spend a few bucks to buy a Faraday Bag to put the phone in.....which accomplishes that same thing.

The thief does not even need to power off the phone to try to prevent the owner from possibly locating it.

but still someone should consider this aspect.

Everyone has, there is nothing you can do about it. lobsgerghost explained to you why it wouldn't matter anyway.

MAriusMKM wrote:

IDK if someone thinked about this ! buttt...is a big big problem.

If will happen to lose your phone, the person who will find it can turn off the device even if is locked and you can't locate him anymore !!!

if you want that feature, check your settings:

It’s probably already enabled, too.

How is that a security problem? If you have a passcode set, they can't get into your phone.

I didnt say that, but your scenario is not a security issue.

That post made no sense at all.