Vibrating swings, vibrating chairs - is there a parent who hasn't relied on the infant-calming effects of good, good, good vibrations? But what a hassle to schlep junior's furniture on a plane trip, even folded up. What if you could take along the buzz minus the bulk? That's what you get with the Tranquilo Mat, a battery-powered roll-up mini-mattress that offers five vibration modes - including two that provide wavelike sounds and pulses meant to simulate life in the womb. (For some reason, these effects are listed as heartbeat sounds, though that's not what they are). The other three modes are low, medium, and more intense levels of a steady gentle buzz.

The battery pack (4 AA batteries not included) is safely secured in a slim, screw-closure plastic case accessed by unzipping the water-resistant nylon liner that permanently encloses the 23.5-by-12-.75-inch polyurethane foam mat. The liner shields the mat and mechanisms from diaper leaks and other infant discharges. A cotton, pillowcaselike cover provides a soft surface and can be removed for washing. Pressing the two button-shaped icons printed on one corner of the cotton cover activates the power- and mode-controlling push buttons, which are inside the mat directly behind the icons.

There are, of course, no guarantees when it comes to crying babies, but the maternity nurse who invented the Tranquilo Mat figured parents would go gaga over an easily totable embodiment of an already popular soothing system for healthy but agitated infants - with the amniotic whoosh effects a bonus. A baby can be placed on top of the mat or swaddled in it while being held.

A smaller, 12-by-9-inch version of the mat works especially well while carrying a baby. It runs on 2 AA batteries (not included) and has all the features of its bigger sibling. Both come with a washable carry sack.

Tranquilo Mat is about $100 for the large size, $85 for the smaller model; at