Elizabeth Taylor had an eye for beautiful jewelry, once declaring "a girl can always have more diamonds." In 2011, her finest jewels sold for $115.9 million at a Christie's auction. Among among the pieces sold that night was a 1961 bejeweled timepiece by Bulgari.

Designed as a serpent to coil around the wrist, it features two hypnotic emerald eyes and tail paved with diamonds. A discreet mechanism opens its jaws to reveal a tiny quartz watch.

Though it was only expected to sell for up to $15,000, the "secret watch" -- so called because the dial is hidden behind a cover -- fetched an impressive $974,500.

Because of the complexity involved in creating a delicate hinged cover, secret watches offer an opportunity for luxury watchmakers to showcase their design creativity, as well as the breadth of their technical savoir faire -- all while answering the demand for multi-functionality.

Secret watches were conceived in the 1920s primarily as a protection for the dial, but also as a more discrete way to keep track of the time among society.

"Having a dial on view was not to everybody's taste, especially if you were wearing fine jewelries, and hiding the piece under some diamonds was a very decent way of having a watch without being perceived of having a watch," says Jonathan Darracott, global head of watches at auction house Bonhams.

"All the brands did some -- Cartier, Omega, Vacheron Constantin, and of course Jaeger-LeCoultre and the Reverso, which is practically a secret watch," he adds. "I think some of the best ones were made in the 1960s and 70s, because they're very much jewelry pieces, with the finest examples being the Bulgari snake watches."

Catherine Cariou, heritage director at Van Cleef & Arpels, says at a time when it may have been considered "indelicate for a lady to look at the time," the brand deployed a wealth of imagination to find discreet and refined solutions, which still seduce today's aesthetes.

Indeed, bejeweled secret watches have enjoyed a renaissance of sorts. Van Cleef & Arpels, who made their first secret watches in the 1930s, unveiled new models as recently as January at the Salon International de la Haute Horlogerie (SIHH) in January.

However, Chadi Nouri Gruber, head of product management at Audemars Piguet, argues they have never truly gone out of style.

"Many brands have been producing those for years, but very discreetly for specific clients. I just think that brands are now communicating much more about them," she says.

Eschewing the world of flora and fauna often associated with feminine timepieces, Audemars Piguet went punk when it released an haute joaillerie cuff watch in 2015, its first secret watch in decades.

A sliding cover reveals the dial, neatly hidden amongst an edgy multi-pyramid contour that is entirely covered with tiny diamonds using snow-setting, a relatively new technique that allows the diamond-setter to play with stones of different diameters and create a more organic design.

"Most of our competitors focus really on the romantic and poetic side of high jewelry creation, which is great because that fits their identity," Gruber says. "We wanted to create something that fits ours. We are a rule-breaker, so we wanted to show we could do high jewelry creations ... but we can do it in a different way."

For its latest creation, unveiled at SIHH 2017, the brand pushed the envelope further with the Diamond Outrage Secret Watch, which has diamond spikes that recall the Alpine peaks of the Le Brassus region of Switzerland, where Audemars Piguet watches are made.

Other brands are entering this niche market for the first time.

During couture week in Paris this past January, Italian jeweler Giampiero Bodino unveiled three timepieces -- all elaborately embellished secret watches -- for the first time. Dior Joaillerie also presented its first secret watches, which had been created as part of a jewelry collection dedicated to the opal, a favorite gemstone of its artistic director, Victoire de Castellane.

The designer used large, oval opals to hide the dials, which are only revealed when the stone is pivoted.

"It just so happens that the bracelets tell time," she said of the watches in a video that highlights their intricate fashioning.

British jeweller Graff Diamonds will also unveil its latest secret watch, called the Princess Butterfly, at Baselworld 2017.

Featuring a highly sculptural diamond butterfly that hides a tiny mother of pearl dial, Graff Diamonds design director Anne-Eva Geffroy says secret watches like this appeal to clients who enjoy the intrigue and element of surprise.

"By the very nature of their design, the gemstones incorporated and the way in which they are set, each watch is a masterpiece, an extremely special and unique piece," she says.

AS FIRST WRITTEN FOR CNN STYLE

Hiding Time: The Artistry of Secret Watches