passwords

Hi guys!! How do you feel about your significant other having a password on their phone that you don't know. Do you think that they have something to hide. Next question... if you ask what the password is and they don't want to give it to you, Does that seem suspicious, even if they allow you to look through their phone When you ask, they just don't want anyone to know their password... What do you think. Sorry if this is confusing... I won't mention which side of my relationship is which so I get 100% honesty