How to know if Activation Lock is on a used iPhone

You can't from the outside.

If you have access to the device and the passcode for it, you can check that no iCloud account is signed in in Settings and that Find My is not turned on in Settings ➜ Apple Account ➜ Find My.

Beyond that, restoring the iPhone and trying to set it up will show the Activation Lock screen during setup if the above steps have not be performed.

The owner / seller should follow the steps in the link below before selling the iPhone.

click here ➜ What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

You'll see it as soon as you turn the phone on. You'll get a screen telling you it's been activation locked, and to enter the email address and password it's asking for in order to turn it back on.

joannachristian wrote:

How do you know if activation lock is on in a used iphone

PLEASE read this --> The All Too Common SAD Reality of Buying … - Apple Community

If you can't see the phone in-person and see that it opens to the Hello Page - DON'T BUY IT.

Apple ID and Activation Lock

iCloud uses Apple ID credentials.

If you do not remember the Apple ID Password then follow the steps given in this Apple Article -> If you forgot your Apple ID password - Apple Support

If you do not remember the Apple ID then follow the steps given in this Apple Article -> If you forgot your Apple ID - Apple Support

If you are the owner or the owner has shared all information with you then to open Activation Lock:- If it is Activation locked, read here --> Turn off Activation Lock - Apple Support Activation Lock for iPhone, iPad, and iPod touch - Apple Support

Learn how to remove a device from a previous owner's account.

If you are not the rightful owner of this iPhone and do not possess the associated Apple ID and password, there is absolutely no way to gain access to the device. Apple’s security framework is designed to prevent unauthorized use, so the only circumstance in which you could unlock the phone is if the original owner willingly provides their credentials. In rare cases, access might become possible if the owner unintentionally removes the device from their Apple ID account, but this is purely accidental and not something you can rely on. In essence, without the Apple ID and password, the iPhone remains permanently tied to its legitimate owner.