Short answer
Fake Clé de Cartier Medium watches exist in large numbers, and most can be screened out in under five minutes with a loupe. Three checks catch the biggest share of copies: the key-shaped crown, the caseback engraving, and the movement. A genuine automatic Clé de Cartier Medium runs Cartier's calibre 1847 MC inside a case of about 35 mm, with a cabochon-set crown shaped like the head of an old key. Copies miss the crown geometry, the engraving depth, or the movement finish, and often all three at once.
What the real watch should look like
Know the target before you start. The Clé de Cartier launched in 2015 and takes its name from that key-shaped crown. The Medium sits around 35 mm across in steel or gold, with a silvered dial, Roman numerals, blued-steel sword hands, a date at 3 o'clock, sapphire crystal front and back, and an alligator strap on a folding clasp. Water resistance is modest, so do not expect a heavy dive-case build. Every one of those features is a checkpoint.
What you need
- A 10x jeweler's loupe
- A bright, diffuse light source
- Digital calipers
- A gram scale
- Reference photos of a genuine Medium from a dealer or auction archive
How to check a Clé de Cartier Medium step by step
- Measure the case across the bezel, excluding the crown. A Medium lands near 35 mm. Copies often run 1 to 2 mm large because the builder reused a generic case.
- Weigh the watch head on its own. Steel Mediums fall inside a narrow band. A copy with a plated brass case feels light and usually reads 10 to 20 percent below the real figure.
- Inspect the crown under the loupe. The key head needs straight, crisp flutes and a cabochon that sits flush with no glue line. Copies show soft edges, uneven flutes, or a plastic bead.
- Tilt the crystal under light. Genuine sapphire shows no distortion at the rim. Mineral glass on a copy shows a faint rainbow ring near the edge.
- Study the dial print. Cartier sets Roman numerals and the signature with sharp, open strokes. Copies smear, thicken, or fill the counters.
- Check the date aperture. It should be cut with sharp corners and no white halo, with the numeral sitting centered in the window.
- Turn the watch over. The caseback must carry a reference number and a serial, both engraved into the metal rather than printed on top. Compare the letterforms against published photos.
- Look at the movement through the display back. The 1847 MC shows Geneva stripes, blued screws, and a rotor engraved with the Cartier name. Copies use undecorated movements, rough striping, or a Miyota or Seiko base.
- Flex the strap and open the clasp. Real alligator has irregular scale shapes and a matte finish. Stamped calf with a printed pattern points to a copy.
- Set the watch beside your reference photo at the same angle and lighting. Lug and bezel proportion errors show up fast this way.
Red flags that settle the question
- No serial number, or the same serial on two watches
- Caseback fasteners that do not match the reference
- Movement marked Swiss made with no jewels or finishing visible
- Total weight well below the published figure
- A price far under the used market for that reference
- Packaging that is generic or printed on thin card stock
Where to confirm
A Cartier boutique or an authorized watchmaker can open the case and identify the movement in minutes. If a seller refuses that step, treat the watch as fake. Keep any authentication record with the watch, since it also protects you at resale.