How to tell if a G-Shock is fake: the module number on the back is the test that actually works

The one test that works

G-Shock is one of the most counterfeited watch lines in the world, and the fakes have moved on. The dial print is sharp now, the bezel text is right, the box and papers look convincing, and the listing photographs are often stolen from Casio. Any guide that tells you to compare the font on the logo is about ten years out of date.

What has not changed is that a real G-Shock is a specific module in a specific case, and Casio publishes which module goes in which model, for free, with a full operation guide for each one. That makes the caseback the one authentication test that is cheap, fast and objective, and it is where this guide starts.

Casio runs enforcement actions against counterfeiters and its regional arms publish warnings naming specific faked references, which is worth knowing for one reason: the models most worth faking are the popular ones. The GA-2100 in particular has been documented as a counterfeit target.

Step 1: the module number

Every Casio digital watch has a module number, usually four digits, stamped or printed on the caseback next to the model reference. It identifies the movement and electronics, not the case. Casio's support site hosts an operation guide for every module, searchable by that number.

The procedure takes two minutes:

1. Read the module number off the caseback. On most references it sits under or beside the model name.
2. Search Casio's operation-guide archive for that module number and open the guide.
3. Check the guide covers the model you are holding, and that the functions described match what the watch actually does.

Module numbers we have verified against Casio or published spec sheets for watches on this site:

Step 2: the markings on the back

After the module, the caseback itself tells you a lot. On a genuine watch the markings are crisp, consistent and complete. Specifically:

• The water-resistance marking. Every G-Shock we rank is 200-meter water resistant, and the caseback says so in Casio's own format, such as WATER RESIST 20BAR. A G-Shock claiming 30 m or 50 m, or carrying no marking at all, is wrong by definition. What the marking means is unpacked in watch water resistance explained.
• The model reference, in full. Not "G-SHOCK 5600" but the complete reference such as DW-5600E or GW-M5610U. Casio uses suffixes precisely, and they distinguish genuinely different watches: a GW-M5610U has Tough Solar and Multi-Band 6, a DW-5600E does not.
• Consistency between back and dial. If the caseback says TOUGH SOLAR, the dial should say it too and the watch should actually run from light. If the dial carries MULTI BAND 6, the module guide should describe radio time reception.
• Screw type and finish. Casio uses four case screws on most G-Shocks, properly seated and evenly torqued, in a finish that matches the caseback.

Step 3: how it behaves

Functional tests are the second-best authentication after the module, because a generic movement cannot fake behaviour that depends on real hardware.

The backlight. Casio specifies the light type per model and it is in the spec sheet: the DW-6900 has an EL light across the whole dial, the DW-9052 a blue-green EL backlight, the GA-2100 a double LED light, the GMW-B5000 a full auto LED light. A fake usually has a single dim LED that lights part of the display regardless of what the model should do.

Tough Solar, if the dial claims it. A real Tough Solar watch charges from any light and Casio publishes a battery-level indicator in the module guide. Put the watch under a bright lamp and the level indicator should respond over time. A fake with TOUGH SOLAR printed on the dial and a coin cell inside will never move.

Radio time, if the dial claims it. Multi-Band 6 watches receive a time signal and correct themselves, and the module guide describes the reception screens and the signal-strength display. Those screens either exist or they do not.

Stopwatch resolution. Casio publishes it: 1/100-second on the GA-2100, DW-9052 and DW-6900, 1/1000-second on the GA-100. A generic module typically runs 1/100 regardless and labels itself whatever the dial says.

Step 4: the physical tells

These are the least reliable checks, which is why they are last, but they are still worth running:

• Weight. Casio publishes a weight for every model and the numbers are specific: 51 g for a GA-2100, 52 g for a DW-5600E, 93 g for a Rangeman GW-9400, 106 g for a Mudmaster GWG-2000. A kitchen scale settles a lot of arguments.
• Button feel. Genuine pushers have a defined click and return cleanly. Mushy, rattly or sticking buttons are the most common giveaway on a watch that otherwise looks right.
• Resin smell and finish. Casio resin has no strong chemical smell and the mould lines are clean. A sharp plastic smell out of the box is a bad sign.
• Strap keeper and spring bars. Fakes economise here first: thin keepers, loose fit, poorly finished spring bars.
• The LCD at an angle. A genuine Casio LCD has good contrast and consistent segment darkness; a cheap panel washes out as you tilt it.

Where to buy so it never comes up

Casio's own guidance to consumers is the obvious one and it is still the right one: buy from authorised retail partners and official channel partners. In practice, for anyone buying online:

• Buy from a seller with a real returns policy, so that a module-number mismatch is a return rather than an argument.
• Be suspicious of a price well under the going rate for the reference. Casio's U.S. catalogue prices moved up roughly 10% in September 2025, so a current-model G-Shock far below the tier it belongs in is a flag. The tiers are mapped in best G-Shock under $100 and best G-Shock under $200.
• Treat collaboration and limited editions with extra care. They carry the biggest price premium and therefore attract the most counterfeiting, which is why the ones worth owning are listed separately in best G-Shock collabs.
• Check the module before the return window closes. Two minutes on the day it arrives.

The picks

If you already bought one

Three things, in order. Document it: photograph the caseback, the dial and the packaging before you contact anyone. Open a return or a dispute with the platform rather than negotiating with the seller, citing the module-number mismatch, which is objective and checkable. And do not have it serviced: a watchmaker cannot make a counterfeit genuine, and the money is better spent on a real one.

The consolation is that the real thing is cheap. The reason counterfeit G-Shocks exist at all is brand value rather than price, and a genuine DW-5600E or GA-2100 costs little enough that buying the authentic watch is almost always the better decision. Where each sits is in best G-Shock watches for men.