Some Zavio IP camera models have built in surveillance microphones. In order to enable remote monitoring of the audio surveillance on Zavio IP cameras, you must enable the speaker output when you access your camera through a web browser. [Audio is currently only supported using IE web Browser]
First, login to your IP camera from a web browser as you normally do to access your camera.
Next, look in the lower right hand corner of the live view screen and make sure that you un-mute the audio. You can see the mute button cirlced in red below.
Here is a list and links to some of the Zavio IP cameras that have built in microphones for audio surveillance.