Does this provide any protection? I've never undergone any sort of 'digital search' do they force you to provide your passcode? Do the forensics tools they use bypass user level protections like pin codes/finger prints?
They can ask. You can refuse. If you refuse they can seize your device. If you are not a US citizen, they can deny you entry to the country.
Read the EFF Digital Privacy guide for the Full Monty: https://www.eff.org/wp/digital-privacy-us-border-2017
Here's some info on it: https://www.digitaltrends.com/mobile/how-to-use-android-9-pi...