Are my phones unlocked?

I asked this a little while ago, then marked it as answered. However, the solution didn't work as I thought...so I'm asking again. Sorry! I don't have a service agreement with Apple, so I can't get them on a chat.

I have 2 hand-me-down i Phones: 5c and 5s. Is there a way for me to determine if they are unlocked, and if not, which carrier they work with? I've been using the 5s with Straight Talk. I never activated the 5c, and don't remember which carrier it was used with prior.

I just got my iPhone 6 🙂 and will probably hand these down to someone else.

Thank you!