There are plenty of legitimate excuses to have a panic setup like that. Even in a situation where it's presence is suspicious, it can't be used as evidence against someone by itself. It'd be like getting pulled over for speeding, and the cop catches you reformatting your smartphone while you're sitting in the car. Sure, it looks guilty as hell, but if he didn't pull you over for anything other than speeding, he can't arrest you, and say you were destroying evidence, since he had no reason to assume anything incriminating was on your smartphone. The act of taking even overly extreme measures to protect your data means nothing by itself, and can't be used against you.
...though he could probably use it as an excuse to search your vehicle. If he happens to find 10 kilos of coke in your trunk, it'll become a whole different story.
It's the same situation with a panic password, equipped with an EMP generator to wipe a harddrive. By itself it means nothing. But if the police have been investigating you because your name and internet activities have been traced to a few prominent child pornography chat rooms, it becomes something that could be thrown in your face in court, with your only defense being a compelling excuse that can be backed up with proof.
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Everyone has rights, even the worst among us.