Baby monitors: an extra set of ears.(Buyers Guide)

Audio baby monitors are not just for babies anymore. Inexpensive (some cost less than $30), small, and portable, they are being used to keep tabs on older kids at play and seniors who need care. Pamela Davol, a dog breeder in Swansea, Mass., uses one to monitor her Labradors in labor.

Baby-monitor technology has recently advanced to include movement sensors, under-the-mattress pads that alert you when movement completely stops for more than 20 seconds. While some parents may find movement sensors reassuring, they are not medical devices and should not be used in place of prescribed heart or breathing monitors to detect conditions such as sleep apnea. Nor should they be relied upon to prevent sudden infant death syndrome. As such, we don't think movement sensors are worth their high price, even though the audio-monitor component of the model we tested rated highly. (See Health Wise, right, for tips on putting your child to bed safely.)

A baby monitor's challenge is to transmit recognizable sound over a distance with minimal interference from other wireless devices. In a variety of environments, we tested seven audio monitors ranging from $20 to $50; an audio/video monitor, $100; and an audio monitor/ movement sensor, $90. All are fine for the basic job of listening in. They differ a lot in other attributes, however. Those differences are noted in our Ratings and in Features That Count (both on page 49).

HOW TO CHOOSE

Pick audio or audio/video. A good audio monitor will let you know whether your baby is awake or asleep, moving or stationary. Our tests showed only so-so picture quality from the one video monitor we rated. You can tell that your baby's eyes are open, for example, but you can't distinguish much detail.

Mind the frequency. None of the baby monitors we tested was immune from static. The closer your monitor's frequency is to that of another device, the more likely you'll hear static or cross talk. You may reduce interference if your monitor lets you switch to a different channel within its frequency band, as do all the models we tested. The Evenflo 3000 and Summer Infant have more separation between channels than the others, for a greater chance of reducing interference.

Choose a monitor that operates in a different frequency band than your cordless phone. Most newer cordless phones are 2.4 gigahertz or 900 megahertz; one of the tested monitors uses 900 MHz.