The short answer

A grand complication is a watch that stacks several high-end functions in one movement: a perpetual calendar, a minute repeater, a split-seconds chronograph, a tourbillon, sometimes all of them. Genuine examples come from a handful of houses and start in the low six figures. A fake grand complication is a replica built to look like one. The dial has the same layout, the subdials sit in the right places, the case has the same bulk, but the movement underneath does a fraction of the work. What you are mostly paying for is the appearance.

That does not mean every replica grand complication is junk. Some are solid watches with a working chronograph or a real tourbillon cage. The point is knowing which parts actually function and which are decoration.

The complications that get faked most

Perpetual and annual calendars

A real perpetual calendar tracks leap years and needs no date correction until 2100. Replicas do not. On most fakes the day, date and month subdials are plain discs, and the month disc advances every 31 days no matter how long the month is. Builders sometimes wire two subdials to the same gear, so the day and the month always move together. A moonphase that completes a full turn in 24 hours is the giveaway. The real cycle runs 29 days, 12 hours and 44 minutes.

Tourbillons

The tourbillon is the easiest complication to fake because it is mostly visual. A real one rotates the balance and escapement inside a cage to average out gravity errors. A cheap fake puts a spinning ring or a small flywheel under an open dial cutout. It turns, it looks busy, and it does nothing for accuracy. Mid-range replicas sometimes carry a genuine Chinese tourbillon. Those do work, though they will not keep time like a Swiss one.

Minute repeaters

This is where fakes fall apart. A minute repeater has racks, hammers and gongs tuned to strike hours, quarters and minutes. Replica repeaters have a slider that does nothing, or a small music-box module that plays a chime unrelated to the time on the dial. If a seller claims a working repeater for a few hundred dollars, it is not a repeater.

Split-seconds chronographs

Most replica chronographs run a standard movement, often a Seagull ST19 or a clone of the Valjoux 7750. A true rattrapante uses two seconds hands and a second column wheel. Fakes add a decorative extra hand that never splits. The test is simple: can the second hand be stopped on its own while the first keeps running?

How to check one before you buy

• Ask for a video instead of photos. Watch the subdials for a full minute. A date that snaps over at midnight is fine. A date that creeps for three hours is not.
• Count the pushers and ask what each one does. Grand complication cases have specific pusher layouts. Unexplained pushers often mean the case was copied from a different reference.
• Check the thickness and the weight. Stacking a tourbillon and a calendar module adds height. A slim case on a watch billed as a grand complication is a warning sign.
• Listen. A minute repeater should chime on demand and sound clear. A tourbillon is nearly silent.
• Look at the caseback. Solid backs hide a lot. If the seller will not send a movement photo, assume the worst.

Price bands and what they buy

• Under $150: quartz or a basic automatic with printed subdials. The calendar is a picture.
• $150 to $400: a working automatic chronograph, sometimes a 24-hour hand standing in for a GMT. No real calendar.
• $400 to $1,000: a real Chinese tourbillon, better finishing, sometimes a working moonphase.
• Above $1,000: better movements and tighter assembly. Even here a true minute repeater is very rare.

Keep the practical side in mind

Replicas are sold as replicas. Wearing one is one thing; passing it off as genuine is fraud, and shipments can be seized by customs. Servicing matters too. Many replica movements have no parts support, so a broken calendar module can turn the watch into a paperweight. Before you buy, decide whether you want a watch that looks complicated or one that is.