Today I want to show you a watch modification that I've been working on. I'm calling it the Data Runner, and it's another F91W mod, this time going the extra mile to make something functional and nice looking.

Like the previous mods that you may have seen me do, this is based on the Casio F91W, and that's down to the fact that it's THE standard for an inexpensive digital watch, striking a good balance between price, features, build quality, and worldwide availability.

The Data Runner name is a nod to the movie Johnny Mnemonic because of the storage features.

- Download Source Files


The first thing you'll notice is that the standard frontplate has been replaced by a minimalist black one. This is actually a piece of 1mm thick acrylic that's been laser cut, and has black UV printing on the back side. I've only tried solid black so far, but I'm guessing you could put all sorts of custom designs on using this technique.

It's secured in place with simple double sided glue tape, the same kind you use for replacing smartphone displays.

Behind the frontplate is a custom 0.6mm thick PCB which acts as an antenna for an NFC chip, meaning it harvests energy wirelessly from say a phone or tablet, and doesn't need a battery. This method also gives you much better scanning range than simply adding an NFC tag or sticker inside, and the two contacts on the back of the antenna allow you to add any kind of NFC chip you can solder and fit inside the watch.

Thankfully there's a little space at the bottom of the watch that's the perfect size for a variety of chips. I chose an 8KB chip and connected it using some super thin enamel coated wires.

The 8KB chips are one of the largest capacity you can buy right now and these are perfect for in-person sharing of public encryption keys, your resumé, or other pieces of data.

One very cool option is to use the chip from a tap to pay card. There are tutorials on the net showing you how to dissolve the card plastic to reveal the chip and antenna that can be soldered into the watch.

I'm pretty sure you can also buy chips with their serial numbers unlocked, allowing you to clone your card.

Either way, it would be pretty cool to be able to make direct payments with the watch, and it's definitely possible. You could probably use the same method for some door access systems as well.

I also experimented with wiring up the LED light button as a way to only initiate the chip once pressed. You can utilize the button motion from the metal of the Casio's custom switches, but it's very fiddly to get working.

As standard for my mods, I also replaced the green LED with a bright white one, but you can leave it if you want. I tested with a red one too but that was hard to see at night, obviously defeating the purpose.

Moving to the back of the watch, you'll notice that it's slightly thicker than a regular F91W, and that's because I've added a micro SD card socket to the inside of the metal backplate.

It's held in place using a simple 3D-printed frame, and allows you to physically carry your important files on your person at all times. With micro SD card capacities reaching over 500GB now, that's a lot of potential data.

One thing to mention is that since the backplate is moved further away from the watch, you'll have to bend up the contacts in order to still have an alarm sound, since the metal backplate cleverly acts as a piezo buzzer.


You have no idea how much messing about and tinkering I've done to these watches over the years. Here are a few other mods I've worked on which didn't quite work out.

I designed a more complex backplate which included 2 NFC chips, buttons and a built in micro SD card reader, that you could read directly by plugging in a micro USB cable. I even made a nice resin printed backplate to cover it, but in the end it made the watch far too thick, and looked a bit silly.

I also created a screen mod which makes the LCD glow in the dark. This is simply done by removing the reflective backing of the LCD with a knife, and putting a piece of glow in the dark material there.

It works, but the problem is it only glows brightly once you've charged it up for a long time in a bright environment. That'd be fine if you're wearing a tshirt outside in the middle of summer, then go into a dark place, but if you have a long sleeve covering the watch, it won't charge up.

Another interesting idea was to install a mini vibration motor instead of the alarm sound from the piezo buzzer, but unfortunately the original watch PCB doesn't have quite enough miliamps to work the motor properly. You could probably modify the circuit or create a mini add on, but then there wouldn't be enough room anyways.


Though the custom frontplate looks good, it is a little fiddly to put in, and it's not quite as clean as a factory manufactured one.

One thing that I'm going to try next is creating an adapter which requires no actual modifications to the watch, so anyone can install it.

It would basically involve creating a flexible PCB, which contains the antenna, the contacts for the chip, the micro SD socket, and a small side actuated button, so the NFC chip will only work when pressed. I think this would be better for security, especially if you're hooking up a tap-to-pay chip inside.

Then you'd be able to place it inside any of the F91W variations that are available, and you'd have a stealth watch with much more functionality than it appears.


All these mods give you a pretty useful little watch, with functionality and looks that you won't see anywhere else. Yes, you could use a "smart" watch, but it will spy on you and has a short battery life in comparison. This thing tells the time, sets alarms, stores data, can potentially pay for stuff, or open doors, and has a battery that lasts for months or years.

I've added the files I have created so far onto the NODE site if you want to experiment. Be aware though, that you need to use a legit Casio F91W, not a cheap knockoff, because the shape of the parts are slightly different.

Anyways, I know it's not the most important project in the world, but hopefully this will be useful or interesting to some of you. I will do another update once I've made the flex PCB version, then if all's well I will add it to the shop.

In the meantime, I just wanna say thank you for watching. I've got some other modded watches on the shop if you wanna support the channel and pick up something cool, and I'll see you in the next video.