The short answer

A convincing fake Omega Planet Ocean Ultra Deep nails the outline first: 45.5 mm wide, roughly 18 mm thick, a domed sapphire that sits proud of the bezel, and those angular crown guards. Where most replicas slip is in the things you can measure with calipers and a scale, plus the small print on the caseback. If you can hold the watch and check five or six specifics, you will know within a minute which tier you are looking at.

What the real watch gives a replica to copy

Omega built the Ultra Deep around its 2019 Mariana Trench dive. The production version is rated to 6,000 m / 20,000 ft, far beyond anything a diver will ever do and far beyond what any replica can survive. The case is Grade 5 titanium on the launch references, 45.5 mm across and 18.12 mm thick, with a ceramic bezel insert, a screw-down crown, and a helium escape valve at 10 o'clock. Inside sits the Co-Axial Master Chronometer caliber 8912 with a 60-hour reserve and 15,000-gauss magnetic resistance.

Those numbers matter because every replica has to fake them. The ones that fake them well cost real money. The ones that fake them badly are obvious the moment you pick them up.

Where replicas give themselves away

Case, thickness, and weight

Titanium is light. A genuine Ultra Deep head feels airy for a 45 mm brick of a watch. Many replicas use 316L stainless instead, so the head feels dense and top-heavy on the wrist. Measure the case with calipers if you can. Anything much under 17 mm or over 19 mm is off. Check the crown guard too: the genuine shape is asymmetric and flows out of the case, while cheap copies look bolted on, with soft edges and uneven brushing.

Dial and lume

The gradient dial, blue at the top fading to black, is hard to reproduce. Bad copies show a hard band where the fade should be, or a purple cast under indoor light. Look at the lume plots: they should be filled flat, not domed, and the outline printing should be crisp under a loupe. On the manta version, the lume manta on the caseback is a good tell. Replicas often print or engrave it shallow and blurry.

Bezel, crown, and valve

The bezel should click through 120 positions with no back play, and the lume pip should sit dead center at 12. Spin it slowly past 6 and watch for a wobbly insert. The crown should screw down without grit, and the helium valve at 10 o'clock should look functional, not like a decorative bump glued into a hole.

Movement

No replica runs a real 8912. Most use a decorated automatic, often an A2824 base with an engraved rotor and fake Cotes de Geneve. That is fine at arm's length, but the tell is the balance: the genuine movement has a free-sprung balance with no regulator index, and a silicon hairspring that is matte black, not shiny metal. Power reserve on a clone lands around 38 to 42 hours, not 60. If it stops overnight, you know what you bought.

Caseback and engraving

Depth rating, reference numbers, the Master Chronometer line, the manta engraving: all of it should be laser sharp and correctly spelled. Replicas leak information here. Wrong font weight, missing accents, a serial that repeats across an entire batch, or text etched so deeply it looks stamped.

Water resistance, said plainly

Every Ultra Deep replica is a desk diver. Gaskets may be present, they may be dry, and the caseback may not seal flat. If you plan to swim, have a watchmaker pressure test it and reseal it first, and even then treat 50 m as the ceiling. The 6,000 m number on the dial is decoration.

Price tiers

• Under $150: wrong thickness, steel case, printed dial, noisy rotor. Fine as a beater, obvious up close.
• $300 to $600: the sweet spot. Correct case profile, decent AR coating, proper gradient dial, clone movement with a decorated rotor.
• Above $700: you are paying for finishing and a better bracelet. The gains are small, and you are close to used genuine money.

Before you pay

• Ask for a weight and a thickness measurement, not photos.
• Ask for a video of the bezel action and the date change.
• Ask which movement is inside and whether the caseback is sapphire or solid.
• Ask about the bracelet clasp and whether it has a diver extension.

One honest note

Selling counterfeit watches is illegal in the United States, and no Omega service center will touch a replica. Resale is thin. Buy it because you like wearing it, not because you think it will hold value.

Bottom line

The best fake Ultra Deep gets the case geometry, the dial fade, and the weight right. Get those three and the watch reads correctly from across a table. Everything else is a loupe conversation.