If you want to buy a used iPhone from someone through a site like Craigslist, it’s a good idea to have a few different ways to tell if that phone is authentic or just not stolen.

But that can be pretty hard to do. Apple wants to make sure that you are buying only real and not stolen iOS devices, so the company has come up with a new tool that will check on the stolen status for you. Here’s how it works.

Using the Activation Lock Website

Apple has just launched a new website that lets users check to see if the Authentication Lock has been switched on when it comes to any iOS device. Activation Locks are part of every iOS device, and owners that report a phone or tablet stolen can activate the lock, and an activated lock means a very useless device that you really don’t want to buy.

You don’t need to have an Apple account to use the Activation Lock website. What you need to do is go to iCloud.com, and look for the Activation Lock website. From there, you can enter the serial number of the device that you are thinking of buying (or IMEI), and click on the Continue button. If you discover that the ‘Find my iPhone’ lock is on, it could mean that the device has been stolen - but, there’s another possibility.

Sometimes, the phone just hasn’t been put to factory reset, and that means that the Find my iPhone button might still be activated.

Why Bother Checking

Even if the device you are thinking of buying isn’t stolen (and you’re sure of that fact), it never hurts to head to the site that Apple has set up, just so you can double-check that the phone hasn’t been locked. There’s nothing worse than buying a phone that has been locked, so just check anyway if you are buying a phone used. Once Activation Lock has been enabled, you can’t use a device unless the original owner enters their Apple ID and Password, which, as you can imagine, is a pain if you are simply trying to buy a used device.

You can deactivate Activation Lock, but you do need to be with the original owner of the device in order to do so. Some second hand sellers will purposely sell locked phones, so that the person buying the phone can’t actually use it once it arrives. For obvious reasons, this renders the phone useless.

So, you may want to be wary if you see a new looking iPhone that is being sold for a ridiculously low amount. It could be that the phone at that amazing price is really a locked phone. Make sure to ask sellers for serial numbers, so that you can check to see if the phone is locked. I’d be wary of anyone not willing to give up a serial number.

The Business Phone Problem

What about business phones that are given to various employees? Sometimes, an employee might leave an office with their personal Apple ID password in tow. The best way to avoid someone leaving your company with an ID is to make sure that person uses a company email address when they first get the phone.

Also, if you can prove that your company owns a phone, Apple should be able to unlock the phone for you at a local Apple store.