CA Penal Code 632a does not prohibit a call on a speakerphone if the other party knows OR if there is noone else listening. However, if the other party expects the communication to be confidential, if a thrid person is present without their presence being disclosed it might be a violation of CA law.
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CA is an "all party" state that requires the consent of everyone on a telephone call or in a conversation to listen to it or tape it, with Penal Code criminal statutes to prevent violations.
As my colleague notes, it's the caller's expectation of privacy that governs, so if a conversation isn't intended to be private, like at a workplace with no walls, then there's no expectation of privacy in those conversations. Sometimes telephone calls made to offices aren't about private matters and aren't expected to be private.
Since there are criminal statutes that enforce these violations, someone whose rights have been violated and who has been damaged by the violation would have to convince law enforcement officials to refer the matter to a DA for prosecution of the infringer.
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