Legalities?

I'm definitely no expert on the subject, but a simple Google search can give you a pretty good idea as to what the legal ramifications are about recording video and audio through hidden surveillance equipment.
In the home, video seems to be legal without audio as long as a camera isn't placed in somewhere private like a bathroom or your nanny's bedroom.
There have been some cases where judges allowed video of nannies and elderly care related videos without the person having known or consented to being recorded. But I would imagine they were doing something bad enough to take it to court in the first place. A general rule is, if it invades someone's personal privacy in a place where they could be changing or doing anything personal...it's a No No!

Audio, however gets a little tricky. As far as I know, it is legal in the following states to record audio when one person in the conversation is aware they are being recorded. Now, if you are one of the people in the conversation, you're covered since you know about the presumably hidden recording device.
Alabama, Alaska, Arizona, Arkansas, Colorado, District of Columbia, Georgia , Idaho, Indiana, Iowa, Kentucky, Louisiana, Maine, Minnesota, Mississippi, Missouri, Minnesota, Nebraska, New Jersey, New Mexico, New York, North Carolina, North Dakota, Oklahoma, Oregon, Ohio, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Vermont, Virginia, West Virginia, Wisconsin, Wyoming
In the states below, it is required to let the other person know they are being recorded. If you don't tell them, you could be sued.
California, Connecticut, Delaware, Florida, Illinois, Maryland, Massachusetts, Michigan, Montana, New Hampshire, Pennsylvania, Washington
Now, in some states, there are exceptions to this rule. If someone is committing a felony, audio recording is generally allowed.

So, what about businesses? Much the same story here. Video is almost always allowed because your investment and employees are being protected. A good way to cover your backside is to put up a sign informing the employees of the possibility of being recorded. Another way to do it is to include a note in the paperwork the employee has to sign when coming to work for the first time.
Audio, again is a different story. It is illegal in all states to record audio without at least one person knowing about it. Of course, this can also be included in the paperwork the employee is signing. It is definitely the best way to limit your legal liability in these situations.

This information is not intended for legal advice. If you aren't sure of the laws in your state, please contact an attorney.