In The cat ate my lunch , the cat, not the lunch, is the active principle of that sentence. In this sense, the subject is the source of an action, has made a decision, is responsible for it. Interpellation makes me a subject in this doubled sense. What that moment of recognition does is pull together, simultaneously, both of those apparently opposed meanings. I am a free agent, and I momentarily give up my freedom to an anonymous call.
Interpellation is a matter of address.
Again, we must pay attention to that basic split, and be careful not to confuse addresser with sender. It is not the sender who has this effect on me. Not any particular law, or even the law of a particular country or place, but just Law in general. It works this way even if the actual speaker should have nothing to do with the real law, or have any real authorisation to stop and query me. And I am not alone.