As a result, women started wearing timepieces masquerading as high jewellery, mostly bracelets, brooches and sautoirs that, for the stylish 20s flapper girl, nestled among her ropes of Chanel pearls and Tiffany & Co. pendants.

Hiding in plain sight, these dazzling watches became enormously fashionable, even though some of the dials secreted under their pretty covers were so small as to be barely legible.

Of course, the rules of etiquette have changed with the times, and in modern society, such attitudes towards checking the time have relaxed somewhat – or at the very least shed their overt sexism.

Nevertheless, secret watches continue to enchant women with their dazzling exteriors and have enjoyed something of a renaissance in recent years.

At Watches and Wonders in Geneva this spring, Chanel, Hermès and Van Cleef & Arpels were among those unveiling a fresh generation of secret watches, and there are rumours that Bulgari has several such novelties to unveil in its high jewellery collection due to drop this month.

Chanel showcased its latest limited edition Mademoiselle Privé Bouton designs with the couturier’s birth sign Leo – the lion’s head depicted in gold and diamonds – protectively hiding a black lacquer dial and quartz movement. Crafted in Chanel’s métiers d’arts workshops, the head is emblazoned on black titanium cuffs, a diamond and onyx sautoir necklace, and a calfskin strap.

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The Chanel sautoir was one of several long necklaces to be unveiled in Geneva, some hiding the dial and some discreetly incorporating it as part of a pendant but inverted so the wearer can discreetly sneak a peek.

Van Cleef & Arpels, which has been making secret watches since the 1920s, expanded its popular Perlée range – originally inspired by 18th-century pocket watches – with ruby, emerald and sapphire covers for the dials.

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Piaget and Jaeger-LeCoultre’s designs differ in that their haute horology workshops made the long, jewelled pendants with the small dials very much on show.

Piaget is a master of creating secret watches and its two Swinging Sixties-style handcrafted high jewellery sautoirs are both similarly decorative and functional. Oval dials hang from twisted gold and diamond chains, with one of the pair featuring Zambian emeralds and a malachite dial. Not so secretive but similarly powered by the ultra-thin 9P hand-wound mechanical movement are the brand’s spectacular Limelight high jewellery cuff watches. Three distinctive designs are inspired by the watchmaker’s 1960s Palace Décor guilloche engraving technique used on luxurious gold bracelets, each with a turquoise or opal dial seemingly exploding out of the side of the cuff.

There is something of a theme for gold bracelets among watchmakers in fact, which links well with the wider current trend for bold yellow gold cuffs in fashion. Hermès, for example, has a new Médor Mini Joaillerie gold and diamond cuff with the dial concealed by a pyramid-shaped stud. It’s a design that relates back to the first pyramid studs used on Hermès belts in the 1930s.

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Van Cleef & Arpels similarly drew on the past, reviving its elegant Ludo bracelet design, which was originally a belt-shaped gold bracelet created in the 1930s honouring Louis Arpels’ nickname, Ludo. The first Ludo watch appeared in 1943 but the maison has updated it with a specially sprung mechanism that you squeeze to lift mystery-set jewelled flaps to expose the time.

Earlier this year Dior and Chaumet also presented new high jewellery watches with the time discreetly hidden.

Playing a sparkling game of hide-and-seek were Chaumet’s Souveraine and Maharani designs which are both traditional-looking wristwatches – but for the fact that their twinkling aventurine dials are veiled by pear-shaped or pave-set diamond motifs that can be slid aside when required.

The Maharani motif is even inspired by a necklace created by the maison for the maharaja of Indore in 1913, one of the Indian princes who spent great fortunes in Paris’ Place Vendôme during that era.

Dior’s artistic director Victoire de Castellane drew on the maison’s couture heritage for inspiration, taking lace as the theme for her latest Dearest Dior high jewellery collection.

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Among the designs is a slender diamond and yellow gold bracelet with a lacy centrepiece featuring little florets picked out in yellow and white diamonds. However, this is no ordinary bracelet as under that flower cover is a diamond pavé-set dial. More directly, La D de Dior Dentelle is a secret watch that dazzles so brightly that it almost keeps the time a secret from the wearer as well.

While ultimately they have a practical function, secret watches have a mysterious allure and hold a special place of honour in the twin worlds of haute horology and high jewellery. Always beautifully handcrafted and often limited to one-of-a-kind pieces, they are beautiful statements of style that might today just prompt a gentleman to inquire politely for the time.