How can I tell if someone unlocked my phone

[AC Question]

I think someone unlocked my phone or sim card is there any way to tell

 

[B. Diddy]

Welcome to Android Central! What do you mean by unlock? Do you think someone unlocked the lockscreen with your PIN/password? Or that someone carrier-unlocked the phone (meaning that the phone can be used on any carrier, not just the one it was purchased from)?