You don't prevent it. That's the thing about security - there is never a such thing as 100% secure. The key is coming up with reasonable expectations and impl

You don't prevent it. That's the thing about security - there is never a such thing as 100% secure. The key is coming up with reasonable expectations and implementing policies to mitigate the risk down to an acceptable level, [EDIT]then putting measures in place to limit damage if those measures do fail[/EDIT]. If I were a third party with access to your device, I could brute force the encryption. There is nothing you can do about it - I will eventually get your password; the trick is whether it will take me a few minutes or a few decades. What's an acceptable time frame to protect the data on your personal cell phone? Do you care if I get the personal data on it 20 years from now or have to spend $2 million in computing power to get it? Unlike me stealing your data, there are very legitimate reasons for law enforcement to have access to devices to carry out investigations. The warrant requirement is a check on abuse. If there's an issue regarding abuse of power (e.g.: bribing employees, intimidating judges, overly broad laws), it would be better for everyone to work to address the real problems than taking away means for law enforcement to investigate actual criminals.