Why are parents spending $99 on this doll?

The Lulla Doll replicates human sounds that help babies feel like they're sleeping beside a loved one.

A doll that is designed to soothe fussy babies at bedtime, which usually sells for 99 dollars, has become so popular that desperate parents are willing to pay triple the price.

One of these sold-out toys actually went for as much as 350 dollars on eBay, while thousands of parents are on a waiting list, reports the Telegraph.

Created by a group of Icelandic mums, the Lulla Doll replicates human sounds that help babies feel like they're sleeping beside a loved one.

As per the toy's website, "When the chest is pressed, Lulla plays a real-life recording of the breathing and heartbeat of a mother at rest. Her name is Gudrun, she is a dear friend, a mother of four and a Kundalini yoga teacher."

Australian distributor Michelle Green revealed that the dolls sell out as soon as they hit shelves.

She said, "It's crazy. I'm packing and they're going out the door as fast as I can get them," adding: "It does sound like Darth Vader but, as I tell mums, most toddlers and babies haven't seen Star Wars."

Chatswood mum Rebecca Ilie, who was one of the lucky ones to buy Lulla late last year before the rush, said that she is impressed with how it put son Max, now 19 months, to sleep, that she ordered two more.

"Max was a dreadful sleeper, he needed to be rocked to sleep, he needed someone with him all the time," she said, adding: "I wore the doll for a couple of days so it smelt like me, then we put it in his cot. His sleep was dramatically improved within days and by three weeks he was sleeping through the night."

She noted, "I actually found the sound quite terrifying, like something out of Exorcist. It's quite loud and I can hear it from outside the bedroom, but it works."