The VTech DM221 audio monitor is the best choice in the category—it's consistently a best seller at multiple retailers, with thousands of positive customer reviews. Losing video is a major sacrifice, of course, but we could see this monitor being a good choice for parents of toddlers who are considering replacing a failing monitor, or people who want a monitor only so they can hear their kid crying out from a distant bedroom.
* Guest Accounts: need to allow guest accounts for grandparents, but absolutely need the ability to turn OFF the microphone for those accounts. The camera is only in the baby's room, but the microphone extends as far as sound travels, and you probably don't want your mother-in-law listening to every discussion in your home. This is a HUGE security feature that is a requirement for anything with guest accounts
There are two basic types: audio and video/audio. Some are analog, others are digital. All monitors operate within a selected radio frequency band to send sound from a baby's room to a receiver in another room. Each monitor consists of a transmitter (the child/nursery unit) and one or more receivers. Prices range from about $25 to $150 for audio monitors and about $80 to $300 for audio/video monitors.