The Casio F91-W - the sign of al-Qaida. Yes, really!
I've a bit of a love for Casio watches, and you can't get any more Casioey than the F91-W. I own a couple of them - I thought I'd lost one at one point so bought another. Then I found the original in a suitcase in the loft. Annoying.
I recently spotted this eBay auction:
I had my suspicions... a genuine F-91W for £3.95 delivered? The 'proof' given by the eBay auction that this is an authentic Casio is that if you hold the right hand button down for a few seconds, CASIo appears on the display. Some early fakes didn't implement this little quirk, but surely the fakers got wise to it and implemented it? By way of comparison, a genuine F91-W from a reputable retailer is currently around the £10 mark. This one, for example, in Argos.
Curiousity got the better of me so I ordered it, and guess what...
It's definitely fake.
I've taken some photos below, comparing the genuine item with the fake. Note that the images are high resolution, so zoom in using your normal method in order to get a close-up look.
Let's look at the face first. The genuine is on the left and the fake on the right. Notice how clear the 'ALARM CHRONOGRAPH' writing is on the real item - you can barely see it on the fake. A tell-tale sign is the tiny 'u' in the bottom right of the face. To print such a small character requires a decent printing process. The fakers don't have a decent process so can't print tiny letters like that, so they've simply made the 'u' much bigger than it should be, in order that it doesn't end up as an unidentifiable blob.
With all the LCD segments visible, it's clear that the fake has added an extra segment, indicated with the arrow.
The strap is a dead giveaway. The fake strap on the right has a horrible tag on it where it's been badly cut from a mould. You can't see any mould lines at all on the genuine strap.
Let's flip it over and look at the back. Look at the screws on the genuine piece - they are Philips screws but they are cut out in one direction such that you could use a flat-head screwdriver to unscrew them. Nice attention to detail. The fake piece on the right has some much larger, Philips-only screws.
Let's look at the circuit boards inside now. They actually look fairly similar. Genuine on the left, fake on the right, as always. You can see that the plating on the fake board is poor - the contacts are nowhere near as shiny as the genuine.
Also worth pointing out here is the three solder blobs, highlighted in red. You can see how they're connected to the crystal. These will almost certainly be used to tune the crystal to get the watch accuracy spot on. Obviously no such tuning has gone on in the fake.
The rear face of the PCB is again as expected. Clearly the genuine on the left is a higher quality.
Lastly, let's have a look at the cases. On the genuine you can see that the buttons have been milled to a point on the end, whereas on the fake they've not bothered. The seal looks much cleaner and precise on the genuine and again you can see the horrible tag on the strap on the fake where it's been cut out of the mould.
So, at this point we're fairly sure that the eBay F91-W is a fake, right? Well, as if you needed any more evidence, this is the bag it came in:
SCRATGHPROOF? Hmm.
I've continued to collect Casio F91-W watches, real and fake and have some interesting findings. Well, interesting to me anyway!
Compare these three watch backs, a genuine and two fakes. One interesting thing to note here is that the screws in one of the fakes has the slots in it that I discussed earlier - the fakers are clearly getting better and better. The screws in the far right fake are definitely still very wrong though.
An interesting point of note is the brushed effect on the steel. On the fakes it runs top to bottom, but on the real one it runs left to right. Probably not enough to ever say for certain that a watch is fake as Casio may change their manufacturing methods from time to time, but it's interesting to note.
The image below demonstrates just how much more readable the real watch it at different angles. You can still make out the time at this obtuse angle on the real one, but all you can see are shadows on the fakes.
The screws in the back are also worthy of note. As you can see, the fakes end in a point whereas the real ones are blunt. Removing a single screw from a watch to check this when checking authenticity seems like a plausible thing to do without affecting waterproofing.
Detecting a fake becomes a whole lot easier if you are prepared to take the back off. Naturally you risk affecting the waterproofing, but if you are reasonably confident that yours is a fake then you won't be taking much of a risk as it's probably not waterproof in the first place!
These three images show the immediate difference between the real and fakes. The middle fake would be passable, if only the white plastic didn't for some reason say 'AA' on it! The right hand fake is a completely different design to the others, immediately obvious.
If we pry out the circuit boards then we can see the ends of the buttons. On the real one the buttons end in a point, not so on the fakes. You can also see the red insert areas on the real which doesn't appear on the fake.
The coin cells powering the watches also are a dead giveaway. The real uses a Panasonic, whereas the others....don't. I've not heard of Jiangnl or Chaoguan, but my assumption is they aren't as good as Panasonic!
Looking at the top of the circuit board, the real watch has a larger LED for illuminatation, and they always seem to have the same surface-mount soldered inductor. The fakes have smaller LEDs and completely different inductors. As before, the real watch has had its crystal tuned with the solder pads in order to improve accuracy, whereas obviously the fakers haven't bothered with this. The epoxy covering the IC in the middle has been accurately placed in the real one, keeping inside the white silkscreen square. The middle fake has gone completely over it.
Now for the rear of the PCBs. The real one on the left looks very similar to the real one earlier on this page, showing that Casio keep them quite consistent. One of the fakes is close, but still different, whereas the other fake is completely different altogether!
The little 'u' printed on the case of the F-91W used to be a sure-fire way of spotting a fake. if it was big then it was a fake, otherwise it wasn't. This has now been complicated somewhat by the fact that the more recent genuine F91-Ws don't have the 'u' printed at all, as you can see below. A large 'u' will always be a fake, though.
Hopefully this has been vaguely interesting. Clearly if you need to prove beyond doubt whether yours is a fake or not then taking the PCB out as if you were changing the battery is the best option - the differences are obvious. Hopefully though, there's enough information on this page such that you can work out without taking the back off if yours is a fake, even if it means removing just one screw.
Andy C
July 2018 (updated June 2025)
andy@burningimage.net