You’re both correct— tptacek is correct in that the 4th amendment is constrained to government search and seizure and there is no positive assertion regarding privacy written into the constitution. But you’re also correct in principle, as the strongest positive assertion regarding privacy (in general) from the U.S. federal gov’t originates in the Supreme Court’s decision in Griswold v. Connecticut from 1965, and Justice William O. Douglas’ reference to privacy as a right inferred primarily as ‘penumbras’ extending from the more specific guarantees of the first 5 amendments.
Edited to Add: All bets are off now, as the court has explicitly reversed stance on this as it regards abortion, which leaves a big precedent for expanding future privacy “exceptions”.
Please note that my original reference to the Constitutions was made to go to the chief social contracts, for brevity: in the case of the USA (which we have picked again to focus on some important cases), condemnation of trespassing, peeping and eavesdropping was part (I understand) of the Common Law from the beginning (inherited from Britain).
They are all cases of instances of breach of a basic principle - license of intrusion is limited, naturally -, which in law needs to be made explicit to sanction specific cases, but remains otherwise evident (in the case of privacy, its breaches are easily farcical).
In Europe, the European Convention on Human Rights (1950), signed by 46 States, specifies in Article 8: «Everyone has the right to respect for his private and family life, his home and his correspondence» (again, an example picked for prominence).
Please also note with reference to your «All bets are off now» that discussion will be made about the boundaries of the principle in practice - the Principle remains.
I don't think the future is all that bright for the privacy penumbra theory of US Con Law. I'm not a lawyer or a Con Law scholar but my understanding is that modern courts have recast the outcome of Griswold into one involving procedural and not substantive rights; of liberty and due process, not of positive rights emanating broadly from the text.
Edited to Add: All bets are off now, as the court has explicitly reversed stance on this as it regards abortion, which leaves a big precedent for expanding future privacy “exceptions”.