Being able to hear conversations and ambient sounds can add a whole new facet to your ability to identify suspects and protect your employees.

Crime

• Audio goes a long way to revealing the intent of the perpetrator during an incident. Take this recent high profile surveillance video for example..., even being low resolution, how beneficial would it have been to have the audio?
• Criminals have been known to call each other by name during the commision of a crime, oblivious to the possiblity they are being recorded. Having at least a partial name would certainly help detectives identify suspects, and would likely aid in prosecution.
• Its not unheard of for a criminal to make or recieve a phone call during the commision of a crime. A custom ring tone or the conversation itself might be enough to lead to a suspect.
• Ambient noises like the tone of a cars exhaust or doors closing etc, can provide valuable information. Unlike a camera that can only see what its aimed at, microphones pick up audio from all directions.

Management

• We all know that the customer is always right. But on occasion a customer may exaggerate or embellish the truth when complaining about how they were treated by an employee. Having the recording of the actual conversation more often than not defends your employees. And should the recording reveal that the customer was indeed right, management has the facts on which to act accordingly.

This list goes on but you get the idea.

There has been a lot of discussion about the legality of recording audio. It varies from state to state but in Colorado the general rule of thumb as I understand it is that audio recording is permissible anywhere that someone would not have a "reasonable expectation of privacy". Or in other words, if a third party bystander can overhear your conversation, its not private. At a store or restaurant counter, or in a hotel lobby, one should not reasonably expect any privacy. On the other hand, any closed room like an office, clinic examination room, restroom, etc., one would certainly have an expectation of privacy. If in doubt, a consultation with your attorney is always a good idea.
Another good idea is to post signage stating that video and audio recording is active on the premises, similar to signage that you see at Denver International Airport... Look for them next time you're there, I'll get a picture next time I am there.