CheckMag | New vintage Casio mod that can give your $20 watch superpowers, like step-counter and Blackjack

Casio’s humble F‑91W (and its metal A158W sibling, curr. $27 on Amazon) has an almost cult following. It’s rugged, affordable, and nostalgically simple - basically a digital workhorse with a 7‑year battery and millions sold. In the words of an r/casio member, the F‑91W (curr. $19.90 on Amazon) is literally the "Honda Civic of watches" for modders. Even its Amazon listing has "over 60,000" high ratings. An engineer-crafted upgrade called Ollee Watch lets you keep that classic look while adding modern smarts. It’s literally a tiny circuit-board swap that turns the F‑91W or A158W into a Bluetooth-connected gadget.

Ollee Watch is the brainchild of a wearable-devices engineer and Casio fan who "didn’t want a smartwatch" on his wrist. He loved the Casio’s simplicity and battery life, but wanted a few smartphone-style features without a giant screen or daily charging. The result is Ollee: a compact PCB that replaces the stock Casio module. In the founder’s words, Ollee is "a 5-minute circuit board swap that can give the watch superpowers." In short, it keeps the vintage Casio look and battery advantages intact, but opens the door to many new functions.

For starters, the clock can now auto-sync via Bluetooth with your phone, and you get world-time, 5-programmable timers, a 1/100-second stopwatch and even sunrise/sunset times by GPS. The alarm gains a snooze setting and hourly chime, and can play custom tunes (yes, one user even a Star Wars melody option). On the health side, Ollee adds an accelerometer to count steps, plus a heart-rate "pulsometer" and ambient temperature sensor, all logged on the watch and sent to the Ollee mobile app.

There are lifestyle benefits as well: a full-color RGB backlight you can tint any hue, a digital compass heading, and even an NFC contact-tag (for sharing a link or ID) in compatible resin-cased models. The tiny gadget also includes fun extras - a flashlight mode, a digital tally-counter (clicker), and even simple mini-games like Pong or Blackjack - all navigated via the Casio’s buttons.

Under the hood, the Ollee PCB packs a modern microcontroller (ARM Cortex) with Bluetooth LE. It runs off a standard CR2016 coin cell: performance ranges from roughly 10 months of heavy use up to 3 years in ultra-power-save mode. By comparison, a stock F‑91W might go 7+ years on one battery, but with far fewer tasks. When you open the Ollee app on iOS or Android, you can configure every setting - alarms, timezones, fitness goals, LED colors, etc. The watch and app keep each other in sync whenever you bring them together.

Getting Ollee Watch into your Casio is surprisingly straightforward. No soldering is required. You simply remove the watch’s snap-on caseback (a small prying tool or knife works), pop out the original module and its battery, and drop in the Ollee board with a fresh CR2016 battery. The unit is designed as a "drop-in replacement". On paper, it’s a quick 5–10-minute job. The kit includes the Ollee PCB and optional NFC tag; you’ll need common tools like a case opener or small screwdriver and a pair of non-magnetic tweezers. After replacing the board, you reseal the case (replace the rubber gasket carefully to keep splash resistance) and pair the watch with the Ollee mobile app. A bit of dexterity is obviously needed to handle the tiny board, but as per early users, the actual swap is "smooth and easy".

As with any third-party mod, opinions vary. A "purist" quipped that "if you want a smartwatch, buy a smartwatch," calling Ollee "a gold medal in the waste of time Olympics". But many hobbyists love it. A commenter on a Casio forum said that the Ollee "took an $18 Casio that’s been loved forever and slipped some brains into it - Bluetooth, steps, sunrise/sunset, custom alarms, RGB backlight… still keeps the classic look… but now it chats with your phone".

Where to buy

The Ollee Watch mod is sold directly from the maker’s website. The DIY circuit board kit is $54.99, and for about $99.99 you can get a complete F‑91W/A158W (new watch + pre-installed Ollee). To be fair, stock watches are extremely common worldwide and can also be pre-purchased separately. The Ollee mobile app is free on iOS and Android, and the developer has a dedicated subreddit and video tutorials (see above) to help new users.