Casio G-Shock GA-B2100 CasiOak vs Seiko Prospex Alpinist
Two divers compared — $100–$150 vs $500–$1,000
Quick Verdict
The Casio G-Shock GA-B2100 CasiOak ($100–$150) offers Casio Quartz (Solar-Powered) precision in the tier below the Seiko Prospex Alpinist ($500–$1,000). The G-Shock GA-B2100 CasiOak measures 45.4mm (48.5mm lug-to-lug, 11.9mm thick) and is rated 200m (20 ATM). The Prospex Alpinist counters with Made in Japan craftsmanship and 200m (20 ATM) water resistance. Both are exceptional divers for their respective tiers.
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Specifications Compared
| Feature | Casio G-Shock GA-B2100 CasiOak | Seiko Prospex Alpinist |
|---|---|---|
| Price | $100–$150 | $500–$1,000 |
| Case Size | 45.4mm (48.5mm lug-to-lug, 11.9mm thick) | 39.5mm |
| Movement | Quartz Module 5689 (Tough Solar + Bluetooth) | Automatic Caliber 6R35 |
| Caliber Type | Casio Quartz (Solar-Powered) | In-House Automatic Manufacture |
| Power Reserve | About 7 months on a full charge without light; about 18 months in power-saving (Casio) | 70 Hours |
| Water Resistance | 200m (20 ATM) | 200m (20 ATM) |
| Crystal | Mineral Glass | Sapphire with Cyclops |
| Case Material | Carbon Core Guard Resin | Stainless Steel |
| Origin | Made in Japan | Made in Japan |
Category-by-Category Analysis
Design & Aesthetics
Casio's design language vs Seiko's approach
The Casio G-Shock GA-B2100 CasiOak features a Carbon Core Guard Resin case at 45.4mm (48.5mm lug-to-lug, 11.9mm thick) with Mineral Glass protection. The Seiko Prospex Alpinist offers Stainless Steel construction at 39.5mm with Sapphire with Cyclops. Both represent their brand's distinct design philosophy and heritage.
Movement & Performance
Quartz Module 5689 (Tough Solar + Bluetooth) vs Automatic Caliber 6R35
The G-Shock GA-B2100 CasiOak runs the Quartz Module 5689 (Tough Solar + Bluetooth) (Casio Quartz (Solar-Powered), About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve) at standard frequency. The Prospex Alpinist uses the Automatic Caliber 6R35 (In-House Automatic Manufacture, 70 Hours reserve) at 21,600 vph (3 Hz). The Prospex Alpinist offers a longer power reserve.
Wearability & Fit
45.4mm (48.5mm lug-to-lug, 11.9mm thick) vs 39.5mm — different wrist presence
At 45.4mm (48.5mm lug-to-lug, 11.9mm thick), the G-Shock GA-B2100 CasiOak has a bolder wrist presence compared to the Prospex Alpinist at 39.5mm. Water resistance differs: 200m (20 ATM) vs 200m (20 ATM).
Value & Cost of Ownership
Casio sits in the lower tier
The Casio G-Shock GA-B2100 CasiOak sits at $100–$150 and the Seiko Prospex Alpinist at $500–$1,000. On the specs that outlast any price: the G-Shock GA-B2100 CasiOak uses Mineral Glass with About 7 months on a full charge without light; about 18 months in power-saving (Casio), against Sapphire with Cyclops and 70 Hours on the Prospex Alpinist. Service intervals are typically 5-7 years for both.
Water Resistance
200m (20 ATM) vs 200m (20 ATM)
The G-Shock GA-B2100 CasiOak is rated to 200m (20 ATM) while the Prospex Alpinist handles 200m (20 ATM). Both offer identical water resistance ratings.
Our Verdict
Casio
G-Shock GA-B2100 CasiOak
Choose the Casio G-Shock GA-B2100 CasiOak if you prioritize Casio Quartz (Solar-Powered) engineering, Made in Japan craftsmanship, and 200m (20 ATM) water resistance. At $100–$150, it delivers Quartz Module 5689 (Tough Solar + Bluetooth) with About 7 months on a full charge without light; about 18 months in power-saving (Casio) power reserve.
Check Price on AmazonSeiko
Prospex Alpinist
Choose the Seiko Prospex Alpinist if you value In-House Automatic Manufacture technology, Made in Japan heritage, and 39.5mm proportions. At $500–$1,000, the Automatic Caliber 6R35 with 70 Hours power reserve makes it a compelling choice.
Check Price on AmazonThe Bottom Line
The Casio G-Shock GA-B2100 CasiOak and Seiko Prospex Alpinist represent two distinct approaches to the diver category — the Casio bringing Made in Japan tradition while Seiko delivers Made in Japan engineering.
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How This Page Was Made
Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.