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Casio G-Shock GA-2100 Series Analog-Digital Black Resin Watch 48.5mm - GA2100-1A

The 'CasiOak': G-Shock toughness in a slim octagonal case — Carbon Core Guard, 200-meter water resistance, and just 51 grams.

The GA-2100-1A takes the octagonal bezel of the original 1983 G-Shock and rebuilds it around a Carbon Core Guard structure — a carbon-fiber-reinforced resin case that protects the module while keeping the watch slim at 11.8 mm thick and light at 51 grams.

It is shock resistant with 200-meter water resistance, an analog-digital display, and a battery rated for approximately 3 years. World time covers 31 time zones, and the watch includes a 1/100-second stopwatch, countdown timer, five daily alarms, a Double LED light, and a full auto-calendar to the year 2099.

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Last updated: November 9, 2026

Specifications

  • 48.5 x 45.4 x 11.8 mm case
  • 51 g
  • 200-meter water resistance
  • Carbon Core Guard

Key specifications as stated on the Amazon listing.

What we like

  • G-Shock toughness in a slim, light case that wears smaller than most G-Shocks
  • 200-meter water resistance suits swimming and everyday wear
  • Approximately 3-year battery life — no charging to think about

What to watch for

  • Mineral glass, not sapphire, so the crystal can mark more easily
  • No smart features — no notifications, fitness tracking, or app
  • At 48.5 mm wide, the octagonal case still wears large on small wrists

Key features

  • Carbon Core Guard structure with a carbon-fiber-reinforced resin case
  • Shock resistant with 200-meter water resistance
  • Analog-digital display with Double LED light
  • World time: 31 time zones (48 cities + UTC), daylight saving on/off
  • 1/100-second stopwatch, countdown timer, 5 daily alarms, full auto-calendar to 2099

Who should buy it

Buy it if you want a tough, light, everyday watch with real water resistance and a classic octagonal look, without charging or smartwatch complexity.

Who should avoid it

Skip it if you want smartwatch features, a sapphire crystal, or a small, dressy watch for formal wear.

Comparison with alternatives

How Casio G-Shock GA-2100 Series Analog-Digital Black Resin Watch 48.5mm - GA2100-1A stacks up against other options worth considering.

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