How social media remade the luxury watch market

A Brazilian aviator and a French jeweler walk into a bar. The year: 1900. The place: Maxim's, the Paris clubhouse for the Belle Époque intelligentsia to discuss matters such as, How much absinthe is too much absinthe? On this day, the question was more practical: How does a pilot tell time on his pocket watch without crashing his airship?

Alberto Santos-Dumont was the son of a French-Brazilian coffee tycoon, and a dashing explorer and aeronaut. His pal, Louis Cartier—another nepo baby as the scion of the Cartier jewelry empire, and a brilliant designer in his own right—proposed a solution: What if a watch could be fastened to his ami's arm, instead of kept in the pocket of his trousers?

This is how the modern men's wristwatch was born.

Cartier debuted the delicate, square-faced Santos in 1911 and has been producing versions ever since. They range from svelte relics to a showy platinum-cased 90th anniversary edition with a salmon dial and indigo Breguet hands that fetched nearly $48,000 at Christie's last year.

"Collectibility-wise, Cartier is probably one of the biggest brands that exists," says Tom Collins, owner of vintage watch dealer the Wrist Watcher Ltd., "but there are so, so many variants, it's hard to pinpoint which is a collector's piece."

There are clues horologists look for, like the number of grams of gold engraved on the back of the two-tone Santos Carrée, a piece Collins recently acquired for his tiny counter in London's tony Mayfair. Debuted in 1978, this particular model represents a significant inflection point in design and mechanics for Cartier. The house recast the Santos in a chunky, sportier silhouette; squared the face (carrée is French for "square"); exposed its screws; and integrated a bracelet in stainless steel and 18-karat gold. It also went automatic.

The Carrée is my favorite Santos, a cuspy chameleon that, depending on styling, can give off last days of disco or Bret Easton Ellis protagonist. When I saw it, I had to have it.

Where I saw it, though, was not at Grays Antique Market, the agora where the Wrist Watcher Ltd. rents space, but while scrolling on my phone during a red-eye from Addis Ababa to Heathrow last spring. On random evenings at 8 p.m. U.K. time on @TheWristWatcher1, 22-year-old Collins drops a cache of treasures to his 260,000 watch-fanatic followers, of which I am one. "Presenting the cleanest Cartier Santos Carrée on the market!" the caption read. I immediately slotted a visit into my London plans so I could take my precious home.