How to know wether my iphone is factory unlocked or not?

I have two iphone 5.one is white and second is black. I recently bought second black iphone.person who gave me said it's factory unclocked but I'm confused wether it's factory unlocked or not. How can I know?

You can chek your mobile factory

Put a new sim in it a different network one if your phone is unlocked it will work and you'll have signal if it doesn't then it's locked

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