A fake Fifty Fathoms 5015 is a counterfeit copy of Blancpain's 45 mm Fifty Fathoms Automatique, and the fastest way to expose one is the movement. The genuine reference 5015 runs Blancpain's in-house calibre 1315, a three-barrel automatic with a 120-hour power reserve. Copies use mass-produced third-party automatics that stop somewhere around 38 to 45 hours, and an engraved rotor plate does not change that. The checks below cover movement, bezel and dial, case and water resistance, paperwork, and the practical and legal cost of owning a counterfeit. Run them in that order and you will know what you are looking at within minutes.

1. Movement and power reserve

The 5015 has a sapphire caseback, so the movement sits on display and the differences are not subtle.

• Genuine strengths: calibre 1315 signed Blancpain, three barrels in series, 120-hour reserve, silicon balance spring, gold rotor with engraved branding.
• Counterfeit weaknesses: a generic Japanese or Chinese automatic under a plated rotor, with decorative screws that hold nothing and finishing that disappears under a loupe.
• Quick test: wind it fully, set it down, and check the time after three days. A 40-hour movement will be dead. A 1315 will still be running.

Use this check first when you buy from a private seller and cannot open the case. Power reserve is the one specification a counterfeit cannot fake with cosmetics.

2. Bezel, crystal and dial

• Genuine strengths: a sapphire bezel insert with the luminescent markers applied underneath the sapphire, so they sit deep and glossy with no edge a fingernail can catch. Dial printing is crisp, and the date window lines up with its aperture.
• Counterfeit weaknesses: lume printed or glued on top of the insert, visible ridges, uneven bevels, and a bezel action that feels loose or gritty when rotated.
• Dial tells: indices that sit slightly proud or lean, text that thickens at the edges, and a date wheel that does not center.

Use this check on photos. Lume depth and the way a bezel edge catches light show up in close-ups taken on a phone, so you can screen a listing before you ever handle the watch.

3. Case, crown and water resistance

• Genuine strengths: 45 mm case, 300 m water resistance, screw-down crown, signed caseback, and a case that feels balanced rather than hollow.
• Counterfeit weaknesses: correct silhouette, wrong weight, soft caseback engraving, sharp lug edges, and gaskets that have never been pressure tested to any depth.
• Risk: diving or swimming with a counterfeit is a reliable way to flood the movement, and no warranty covers the result.

Use this check when the watch is in your hand. Weigh it, run a fingernail along the lugs, and look at how the crown threads engage. Cheap threads bind in the first half turn.

4. Strap, box and paperwork

• Genuine strengths: signed sailcloth or rubber strap, correct buckle hardware, Blancpain box, warranty card, and a service record an authorized dealer can confirm.
• Counterfeit weaknesses: generic strap hardware, a box that photographs well and feels wrong, and paperwork with no dealer, no serial history, and no service behind it.
• Reality check: Blancpain does not sell through replica channels, so a new-looking 5015 at a fraction of retail is counterfeit, stolen, or both.

Use this check last, because it is the easiest to fake in an online listing and the hardest to argue with in person.

5. What a counterfeit actually costs you

• Pros people cite: the Fifty Fathoms look at a small fraction of the price of the real reference.
• Cons: no warranty, no parts supply, watchmakers who decline the work, near-zero resale, and water resistance you cannot trust on a watch built for diving.
• Legal: counterfeit goods that infringe a U.S. trademark can be seized and destroyed at import, and trafficking in counterfeits is a federal offense.

Use-case recommendation: if what you want is the design rather than the name on the dial, a legitimate dive watch at the same budget will keep its water resistance, hold some value, and can still be serviced in ten years. If you want the 5015 itself, a pre-owned example with papers from a reputable dealer is the only version that keeps the 120-hour movement, the sapphire bezel, and the 300 m rating that make the reference worth owning in the first place.