The police come to arrest you, and you quickly lock your phone and turn it off. You know they’re going to want to look through it, and that’s the easiest way to make it impossible. If you refuse to tell them the password, then they can’t get in. It doesn’t matter if you have anything to hide or not. Your privacy is still secure, right?
Maybe. There are a lot of things to consider. To start with, remember that your phone’s information is likely on the cloud, as well. With the right warrants, the police can talk with the companies that you use to get the data without actually opening the phone at all. For instance, Facebook may tell them what messages you sent or Apple may tell them what photos you took. It’s not always up to you alone.
Now, the police can’t illegally search your phone without a warrant, as noted under the 4th Amendment. But the next thing to consider is that other people may have access to the same information. For instance, maybe you sent a text to a friend. The officers want to read it. You refuse. If they ask your friend, though, that friend can show them the text message that they got from you. In that case, the 4th Amendment does not help you at all.
In short, it’s wise to be careful about everything that you do on your phone. Remember that the data could quickly get out of your hands. You need to know all of your legal rights and how to protect your own privacy.