As a general rule, employers must provide notice, in writing, to all employees that audio/video surveillance is being used and where it is being used at the work premises. That having been said, there is no “expectation of privacy” in public areas such as lobbies, conference rooms, stairwells, etc., so recording conversations in these areas is legally permissable. Otherwise, recording without workers' consent is illegal. As these laws can vary from state-to-state, to be certain of all of your rights, you can contact your state's department of labor and/or consult with a local employment law attorney.