Only if you are an active participant in a conversation may you record without notice to the people whose conversations you are recording. Otherwise, there IS an expectation of privacy, even in a public venue like a restaurant, and you may be liable for lawsuit if you record without notice.
Surveillance cameras are recognized and expected and they are usually not hidden; this provides at least constructive notice of the recording (also, sound is rarely recorded on surveillance cameras). This is a very, very different situation from clandestine sound recordings.
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I believe Washington like Illinois and California's laws prohibits the recording of communications unless all parties to the conversation consent.
See my Legal Guide Recording Conversations in Illinois
You need a lawyer because I do not practice in WA (I am in Chicago, IL). Check with a lawyer in your locale to discuss more of the details. Twelve states like Illinois require all party consent to record.
The statutes are at this link: http://apps.leg.wa.gov/RCW/default.aspx?cite=9.73 .
Violators can end up in jail. See RCW 9.73.080 (Penalties).
Good luck to you.
Again, check with a lawyer in your locale.
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