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Casio G-Shock GA-B2100C-9AER Bluetooth Solar Yellow Strap Watch - W17318
Ref. GA-B2100C-9AER
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Stepping up in the same dial colour
The GA-B2100C-9AER is the answer to a straightforward question: what does the GA-2100 — the "CasiOak", with its octagonal bezel that drew obvious comparisons to a certain Swiss sports watch — look like once you add solar charging and Bluetooth without disturbing what made it work? The answer, at 11.9mm thick, is that it looks almost identical. The Bluetooth link handles automatic time synchronisation from a paired phone, and the Tough Solar system draws from any light source, so the combination quietly removes the two main reasons to open the caseback on a G-Shock. At 45.4mm wide, the integrated architecture and Carbon Core Guard construction keep it far flatter and lighter than the figure suggests — 52 grams on the wrist, and slim enough to pass under a cuff. The yellow resin reads as a deliberate colour choice rather than an afterthought: loud against the black ana-digi dial, immediately legible, and consistent with the G-Shock 5600 palette this colourway draws from. The quick-release spring bars mean the strap can be swapped without tools, which matters when you own something this colour and occasionally want something quieter.
- Reference
- GA-B2100C-9AER
- Brand
- Casio
- Collection
- G-Shock
- Case size
- 45.4mm
- Case thickness
- 11.9mm
- Case material
- Resin
- Case shape
- Octagonal
- Dial
- Black
- Crystal
- Mineral
- Movement
- Solar
- Functions
- Day-date, Stopwatch, Countdown timer, Alarm, Backlight, World time, Perpetual calendar, Solar powered, Bluetooth, Dual display
- Water resistance
- 200m
- Bracelet / strap
- Rubber strap
- Strap colour
- Yellow
- Clasp
- Buckle
- Lume
- Luminous
- Retailer
- F.Hinds
Additional specifications
- Lug-to-lug
- 48.5mm
- Strap
- Interchangeable
Learn more about Casio
Tadao Kashio founded Kashio Seisakujo in Tokyo in 1946 as a machine shop. The company's first success was a finger ring that held a cigarette, and its second was the 14-A of 1957 — the world's first all-electric compact calculator, which used solenoids rather than gears.
Casio entered watchmaking in 1974 with the Casiotron, a digital watch with an automatic calendar that knew the varying lengths of months. The company approached watches as an electronics manufacturer rather than a horological one, and that difference produced the G-Shock.
The G-Shock came from a single engineer, Kikuo Ibe, who broke a watch his father had given him and set out to build one that could not break. The specification was three tens: survive a ten-metre drop, ten bars of water pressure, and ten years of battery life. It took over two hundred prototypes, and the solution was suspending the module inside the case on a cushioned internal structure rather than mounting it rigidly. The DW-5000C shipped in 1983.
It became one of the most durable product designs in any category, adopted by militaries, emergency services, and skateboarders alike, and Casio has since added solar charging, radio and GPS timekeeping, Bluetooth, and full-metal and carbon variants.
Casio also produces the Edifice, Pro Trek, and Oceanus lines, and remains an independent Japanese public company.
- 1946
- Tadao Kashio founds the company in Tokyo.
- 1974
- The Casiotron is Casio's first digital watch.
- 1983
- The G-Shock DW-5000C survives Kikuo Ibe's three-tens brief.
- 1994
- The Frogman extends G-Shock to ISO dive certification.
Also in 7 collections
This watch appears in the Casio G-Shock range (84), Back in Stock (4,683), Watches 44mm and Over (827), Sports Watches (800), Dive Watches (568), Solar & Kinetic Watches (208) and Dive Watches Under £300 (93).
Manufacturer’s guarantee
What the specifications mean
A watch built to be worn hard and got wet.
Strengths
- 200m water resistance, rated for actual diving
- 48.5mm lug-to-lug keeps the 45.4mm case wearable
- Luminous hands and markers for low light
- Second time zone for travelling
Worth knowing
- 45.4mm is a large watch with real presence
Casio G-Shock GA-B2100C-9AER Bluetooth Solar alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification | GA-B2100C-9AER | AW0110-82L | RZ515AX9 |
|---|---|---|---|
| Price | £139 | £149 | £100 |
| Case size | 45.4mm | 44mm | 43.8mm |
| Water resistance | 200m | 100m | 100m |
| Movement | Solar | Solar | Solar |
| Strap | Rubber strap | Stainless steel bracelet | Leather strap |
| This watch |
|
|
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 200m it is rated for swimming, snorkelling and recreational diving.
Water resistance explainedWill the glass scratch?
It can, over time. Mineral glass handles daily wear but will pick up fine scratches that sapphire would not.
Sapphire, mineral and acrylic comparedDoes it need a battery?
No. It charges from light, and the cell behind that is designed to last a decade or more.
Quartz, automatic and solar comparedWill it fit my wrist?
Lug-to-lug is 48.5mm, which suits wrists from roughly 16.5cm (6½ inches) upward.
Lug-to-lug decides fit more than case diameter does.
How to size a watch to your wristIs it a men's or women's watch?
Listed as unisex, and at this size it suits any wrist that takes the dimensions.
Cheapest place to buy
F.Hinds is the only UK retailer we track stocking this reference, so there is nothing to compare it against today.
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