Really? All I can find[1] seems to indicate all parties need to consent:

"4. The term 'interception' means to secretly hear, secretly record, or aid another to secretly hear or secretly record the contents of any wire or oral communication through the use of any intercepting device by any person other than a person given prior authority by all parties to such communication..."

[1] http://www.malegislature.gov/Laws/GeneralLaws/PartIV/TitleI/...

If you tell them you're doing it, it's not secret.

What about the "given prior authority by all parties" part?

Read it again. That's an exception for the "no secret recording rule"; it's not an extra requirement.

They usually don't have to believe what the law is when many citizens will easily bend at the sight of officer intimidation because they don't actually know the law.

Which is a shame.