G-Shock GA-2100 ‘CasiOak’ – versions and how to choose
The Casio G-Shock GA-2100 is a slim analogue-digital G-Shock with an octagonal bezel, launched in 2019. Watch enthusiasts have nicknamed it the CasiOak. The series has several versions: the standard GA-2100, the solar-powered GA-B2100 with Bluetooth, the smaller GMA-S2100 and the metal-bezel GM-2100. In this article, we explain their differences and which one suits you.
Where does the GA-2100’s shape come from?
The first G-Shock, the DW-5000C, was released in 1983. According to Casio, the octagonal shape has been part of G-Shock since the very first model, and the GA-2100’s bezel carries it forward. The GA-2100’s appearance is therefore no passing fashion idea, but G-Shock’s own oldest shape in analogue watch form.
Casio describes the idea behind the GA-2100 simply: a slim, compact and simple watch that challenges the idea that a G-Shock always has to be large and bulky. If you are interested in how the G-Shock story began, read our article about the square G-Shock DW-5600.
Slim, but still a G-Shock
The GA-2100’s case is around 11.8 mm thick. According to Casio, it was the thinnest analogue-digital G-Shock when it launched. Two solutions make the slim case possible:
- Carbon Core Guard – the case is made from carbon-fibre-reinforced resin, protecting the movement from within. This allows a smaller case without compromising shock resistance.
- A thinner module – Casio made the movement’s components smaller and packed them more closely together to make the watch thinner.
The models compared here are shock-resistant and have a water resistance rating of 200 m (20 bar). This means swimming and rain are no problem. Read more about watch water resistance.
Versions: GA-2100, GA-B2100, GMA-S2100 and GM-2100
All four versions share the same octagonal shape, but differ in power source, size and material.
GA-2100 – the base model
The GA-2100 is the simplest version in the series, with a carbon-fibre-reinforced polymer case and resin strap, weighing 51 g according to Casio. The hands show the time, while the small display shows the date or digital time. It also has world time, a stopwatch, a countdown timer, five alarms and a double LED light illuminating both the dial and display. The strap can be changed using a small lever, without tools.
Many colour versions are available. For example, see GA-2100-9A9ER or GA-2100K-1AER.
GA-B2100 – solar power and Bluetooth
The GA-B2100 looks almost identical, but has more technology inside. The watch charges from light (Casio calls this Tough Solar) and connects to a phone via Bluetooth. You need Casio’s CASIO WATCHES app on your phone. The app sets the time automatically, lets you choose from around 300 world-time cities, set reminders and use the watch to find your phone.
The hands move out of the way when needed to make the display easier to read. According to Casio, the case dimensions are almost the same as the GA-2100’s (11.9 mm thick, 52 g), so there is barely any difference on the wrist. Example: GA-B2100C-9AER.
GMA-S2100 – the smaller version
The GMA-S2100 is a smaller, more compact version of the GA-2100. Casio says the construction is just as durable, but the watch is designed for a slimmer wrist. It measures 46.2 × 42.9 × 11.2 mm and weighs 41 g. It suits women, young people and men who find the standard GA-2100 too wide. For example, see GMA-S2100BA-4AER.
If you are unsure whether the large or small version will fit, see our guide to choosing a watch size.
GM-2100 – a metal bezel
The GM-2100 is based on the GA-2100, but has a stainless steel bezel. The top surface is brushed and the sides are polished, giving the watch a dressier look. Inside is G-Shock’s characteristic hollow construction, which absorbs shocks. The metal makes the watch heavier: 72 g according to Casio. An example of a version with a dark blue bezel is GM-2100N-2AER.
Comparing the versions
| Model | Dimensions (length × width × thickness, mm) | Weight | Distinguishing feature |
|---|---|---|---|
| GA-2100 | 48.5 × 45.4 × 11.8 | 51 g | base model, carbon-fibre-reinforced polymer case |
| GA-B2100 | 48.5 × 45.4 × 11.9 | 52 g | solar power and Bluetooth |
| GMA-S2100 | 46.2 × 42.9 × 11.2 | 41 g | smaller and more compact |
| GM-2100 | 49.3 × 44.4 × 11.8 | 72 g | stainless steel bezel |
Dimensions are from Casio’s official product pages (GA-2100-1A1, GA-B2100-1A1, GMA-S2100-4A2, GM-2100-1A). They may differ slightly between colour versions; exact figures are listed on each watch’s product page.
Which GA-2100 should you choose?
- You want a simple, lightweight everyday watch – choose the GA-2100.
- You do not want to set the time yourself – choose the GA-B2100. The watch charges from light and gets the correct time from your phone.
- You have limited space on your wrist – choose the GMA-S2100.
- You also want to wear your watch with a blazer – choose the GM-2100. The metal bezel looks dressier.
What should you wear with the GA-2100? Its simple shape makes it more than just a sports watch. A black or grey version works with jeans, a jumper or a simple shirt. The colourful versions are great for summer and casual wear. The metal-bezel GM-2100 is better suited to the office and a blazer.
We compare all G-Shock series in the article choosing a G-Shock.
Buy the GA-2100 from Käekellad.ee
We are an authorised Casio retailer. You can find all GA-2100 series watches in here. We deliver watches to parcel lockers (SmartPost, Omniva, DPD), with free delivery on orders of €50 or more. All watches come with a 2-year warranty and a 14-day right of return. If you are unsure which version to choose, write to us at info@kaekellad.ee.