It's not the password they want, it's the evidence in side the "safe" that your password protects.

You're compelled to provide access. You could probably make a legitimate case for not actually revealing the password if you provided access for them.

damn. that's a really good point, but i still think it'd fall under the 4th. A password is closer to providing a key to a locked door rather than testimony.

It would be interesting to know if there was ever a hybrid case where there was a password-protected door with a numeric keypad, and someone refused to give the pw. I'd assume in a case like that, however, the cops would just smash shit out of it.