Chapter 1 - Phone Locks
First, a note on the law in regards to whether you can be forced to unlock your phone. US law is currently interpreted as "you cannot be forced to unlock your phone using something you know, but you can be forced to unlock your phone using something you are or something you have". What does this mean? Basically, you cannot be forced to unlock your phone for police using a PIN code, password, or pattern lock. However, if you use a face ID lock or a fingerprint lock, police can (with a court order) unlock your phone by holding it up to your face or pressing your finger against the phone's fingerprint sensor. Additionally, if a password, PIN code, or pattern is written down, you can be forced to turn it over to police. For more information, see https://jsberrylaw.com/blog/can-police-officers-force-you-to-unlock-your-cellphone/
Fingerprint and face unlocking should ABSOLUTELY be disabled on your phone.
Whether you can be forced to unlock your phone is only half of the equation. Regardless of whether you can be forced to unlock your phone, with a warrant, police are allowed to try and hack their way into your phone. The type of lock used on the phone makes a huge difference in whether a phone can be broken into. Police have access to forensic tools that try to guess the pattern, PIN, or password.
Pattern locks are the least secure locking mechanism - the patterns can usually be guessed by forensic tools. PIN numbers are more secure than patterns but less secure than passwords. Passwords are the most secure option to lock your phone - we strongly recommend that passwords are used to lock your phone. Passwords should be at least 12 characters long and contain a mixture of upper case, lower case, numbers, and special characters. Google has a page with excellent advice on how to select a strong password - https://support.google.com/accounts/answer/32040
Make sure your Google and / or Apple ID passwords are strong as well - it should be a minimum of 12 characters with at least one of each of the following - upper case, lower case, numbers, and special characters. Make sure the password is nothing that can be guessed, such as a pet's name, child's name, birthdate, or any word in a dictionary.
On an Android phone, launch Settings and select Security. Select Fingerprint Unlock and delete any stored fingerprints. From the Security menu, select "Screen Lock" and enter the old screen lock (PIN or pattern), then choose "Password" at the "Choose a new screen lock" page. Follow the prompts to enter and confirm your new password.
On an iPhone, launch Settings and select "Face ID and Passcode". Enter your old passcode. Turn off Face ID for everything. Scroll down and select "Change Passcode". Enter your old passcode. Select "Passcode Options" and select "Custom Alphanumeric Code". Enter and confirm your new password.
To change your Google password from an Android phone, launch the "Google" app and click on your photo in the upper right corner. Select "Manage Your Google Account". Select "Security" (you may have to scroll to the right to see it), then under "Signing into Google", select "Password".
To change your Apple ID password from an iPhone, open Settings and select your account at the top. Select "Password and Security" and "Change Password". You will have to enter the iPhone passcode, then are able to change your Apple ID password.
DO NOT SELECT A PHONE UNLOCK PASSWORD OR APPLE ID / GOOGLE PASSWORD THAT YOU USE FOR ANY OTHER APP OR WEBSITE.
Unfortunately, there is a way to break into any iPhone from the iPhone 5S through the iPhone X. An exploit called checkm8 can be used to access the data on the iPhone - THERE IS NO WAY TO PROTECT AGAINST CHECKM8 IF YOU HAVE AN IPHONE 5S THROUGH IPHONE X REGARDLESS OF IOS VERSION. If you have an iPhone 5S through iPhone X. please know that police can access all the data on your phone. Consider replacing the phone with an iPhone 11 or newer or with an Android device.