What is Anti Evil Maid?

Thank you for the clarification. It is easy to write of things that are obvious to a more expert person, and not clear to those of us who have not experienced trying to implementing a solution which is vague to them.

I have been trying for some time to wrap my head around this, but still have a ways to go.

Can Heads/AEM detect all hardware attacks? For example, I’ve heard that it may be possible for an attacker to remotely modify peripheral firmware such as in the NIC. Is that something Heads or AEM can detect?