It is exactly a year since Runa, the Osaka-based toymaker, made the first sale of its Ecohime toilet-noise masker. This portable gadget was born as a convenient substitute for the non-portable equivalents, commonly found in restrooms around Japan that make white noise to drown out the sounds of lavatory activities.

In the last year it has sold 110,000 units, each at ¥1,260, so in celebration of this uniquely Japanese success story, here is a little history of Japanese toilet culture, where it has been and where it is headed.

Otokeshi-no Tsubo at the Yakage Folk Museum in Okayama Prefecture.

Ladies toilet culture through the ages

It turns out that in Japan there is a long tradition of masking the noises made when using the toilet, and the lineage of this device goes back as far as the 19th century. The first of its kind was a big bronze urn filled with water, called Otokeshi-no Tsubo -- "urn that covers sound". To create the masking effect, a plug would be raised from the top of the urn, allowing a stream of water to rush out of the dragon's mouth below. But it was only high-ranking officials who could enjoy this luxury.

It was sometime during the 20th century that Japanese women figured out an easier way to do this is by flushing twice (the first to conceal that which followed). But this took a toll on the water supply, so in 1988 the toilet maker Toto introduced the Otohime -- "princess sound" -- which can be found across the country mounted on women's restroom walls or on the control panels of high-tech toilets. When activated, it plays a flushing sound, keeping the noises of you-know-what inaudible.

A wall-mounted Otohime in a woman's restroom.

Maintaining beauty

For cultural reasons, this matters a great deal in Japan (the only other place it's sold is in South Korea). Shigenori Yamaji, a toilet scholar who has published three books on the subject, says, "Japanese people are very sensitive to sound," which is why some women feel shy about others hearing their business in the bathroom. Yamaji explains that by sparing themselves and those within earshot this discomfort, their beauty is maintained.

The 21st century incarnation made its debut one year ago when Runa started selling the pocket-sized version. Brisk sales showed it filled a niche in the sound-covering-gadget market, and imitators soon followed.

Rose Ecohime: the first one produced in July 2009.

Runa's spokesperson, Hidemi Fujioka, explains that they decided to call it Ecohime to draw attention to its eco-friendliness. "What's unique about the Ecohime is that it fuses fashion and environmental awareness," she says. It's also well camouflaged. Strapped onto a cell phone, dangling with other cutesy accessories, no one except a fellow purchaser would know its purpose. The gadgets are available at major stores like Loft, Tokyu Hands and Yodobashi Camera.

So it looks cool, conserves water, and eliminates embarrassment. What more could you want from a gizmo?