And where did you read this exactly?

No, it's not a legal recording unless he was actually aware that he was being recorded. It doesn't matter whether your phone beeps, chirps, tweets or sings Nessun Dorma - unless he's actually made aware that he is being recorded, it's a no-go.

(As an example, my house phone "beeps" to the other person when the phone is about to run out of charge, when another caller is trying to get through...many reasons. See where I'm going here?)