That can't prevent a malicious device which act like harmless for the most time, but do evil thing on certain conditions are met. You may found the evidence of

That can't prevent a malicious device which act like harmless for the most time, but do evil thing on certain conditions are met. You may found the evidence of malicious act after it has happened, but often it's too late. If Amazon is directly responsible for Amazon Echo's malicious act, you can blame Amazon. But if the attacker was government spy agency, you're out of lack. Just don't use these devices which cannot be examined thus cannot be trusted.