Welcome! Thank you for your question.
There are two components to your surveillance issue. Video and Audio.
For Video, you can perform video surveillance (hidden or not) in any room of your business so long as it is not in a place where the employee has a reasonable expectation of privacy. There is a federal law that prevents surveillance in an area where a person has a reasonable expectation of privacy. This would include a bathroom and possibly the employee lounge if it is used as a private dressing room at times.
For Audio, it requires two party consent in Washington for audio surveillance. This means that all parties being recorded with audio must consent to the recording. This would include anyone that enters your lobby and employees. If the audio recording is conspicuous then consent can be implied. However, you cannot hide the fact that you are recording audio, even in a public location like a lobby.
The best practice in audio or video recording is to provide clear notice and get consent from all your employees. This can be done as part of the standard employee manual if you have them sign off on employee policies
I would be concerned with customers not being able to consent to audio recording if you are recording audio in your lobby. You can always get employee consent. However, consent of everyone that enters your lobby may be practically impossible. Remember, for any audio recording (hidden or not) you must get consent.
I cannot provide you with legal advise. I have provided you with information about the law related to your question. My answer, and any information that you find online, should not take the place of having a consultation with a lawyer in your area to advise you regarding your specific issues.
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