Sustainability is unquestionably important to the future of humanity, and countless different industries are currently in the process of transitioning toward renewable resources and reducing their environmental footprints. In some instances, these efforts are simply thinly veiled attempts at greenwashing, although others are legitimate actions that help promote a more environmentally conscious existence, and Casio has been significantly expanding its use of eco-friendly materials while also boasting about it far less than other brands that are simply making a few watch straps out of recycled fishing nets. As a showcase for renewable materials, Casio has created the G-Shock COEXIST collection, which places sustainability directly in the spotlight, and the recently announced GAB2100CT-5A featured here expands upon the core platform of the brand’s highly popular G-Shock 2100 series “Casioak” to create a fresh take on this familiar design that also offers the added convenience of solar charging and Bluetooth connectivity.

From a core design and functionality standpoint, the new Casio G-Shock COEXIST collection GAB2100CT-5A is essentially the same watch as the solar-powered and Bluetooth-equipped Casio G-Shock GAB2100-1A that first debuted in 2022. This means that once you look past its rather distinct brown-colored exterior and eco-friendly materials, you will find the same Carbon Core Guard internal middle case, which incorporates carbon fiber into its construction for superior rigidity and durability. Similarly, the top of the case gets fitted with a flat mineral glass crystal, while the reverse side receives a solid screw-on stainless steel caseback, and just like the rest of Casio’s G-Shock collection, the COEXIST GAB2100CT-5A features 200 meters of water resistance to offer ample protection against virtually all forms of moisture contract. Four stainless steel buttons located around the side of the case offer access to the movement, and though the caseback itself is incredibly similar to what you will find on many other G-Shock models, this particular version features quite a lot of text, and the quantity of markings is enough to even rival what can be observed on military-issued watches. 

Just like the standard G-Shock GAB2100 series watches, powering the COEXIST collection GAB2100CT-5A is Module No. 5689, which is an analog/digital hybrid movement that offers the usual suite of G-Shock features, such as a stopwatch, alarm, countdown timer, automatic calendar, world time function, and LED backlight. Additionally, unlike Casio’s entry-level movements, Module No. 5689 is solar-powered, and it also includes Bluetooth connectivity, which allows you to synchronize the GAB2100CT-5A to your smartphone or tablet and use the Casio Watches app to configure its various settings, rather than engaging in the normal and slightly tedious process of holding and pressing the four physical buttons on the watch. When fully charged, the optional power save function will allow Module No. 5689 to run for up to approximately 18 months in total darkness, and its Bluetooth-synchronized timekeeping provides the G-Shock COEXIST GAB2100CT-5A with both an easy setup process and a true set-it-and-forget-it ownership experience.

Where the Casio G-Shock COEXIST collection GAB2100CT-5A differs most from its siblings regards the materials of its components. The brown rubber bezel is constructed from a bio-based resin produced by renewable organic resources, and the fabric strap is constructed from traceable organic TRUECOTTON, which means that Casio knows the exact farm and spinning mill that is responsible for producing the material. Additionally, the strap is colored using a special dye from FOOD TEXTILE, which is a project that creates natural dyes from products that would otherwise be discarded as food waste, and the unique khaki gray color of the strap fitted to the G-Shock GAB2100CT-5A is achieved by using a dye extracted from echinacea that consists of more than 90% natural ingredients. While the COEXIST collection’s use of these renewable materials is intended to shine a spotlight on these sustainable alternatives, Casio has already been using bio-based resin in some of its other watches, such as the Casio Pro Trek PRW6900BF-1 Bonfire, which uses two different types in the construction of both its case and strap.

In terms of dimensions, the case of the Casio G-Shock COEXIST GAB2100CT-5A measures 45.4mm in diameter by 11.9mm thick, and it has an official lug-to-lug profile of 48.5mm. However, because the fabric strap attaches to the case with brown resin lug adaptors, the actual lug-to-lug profile of the watch ends up being approximately 60mm. While the lug adaptors do angle downwards a considerable amount to help mitigate the perceived size of the watch, they do not bend or articulate in any type of capacity, and this means that the COEXIST collection GAB2100CT-5A wears noticeably larger than other G-Shock GAB2100 series watches that are fitted with standard rubber straps. Just like a number of G-Shock watches, the lug width of the case is a fairly compact 16mm, although the brown bio-based resin lug adaptors quickly flare out to meet the edges of the bezel before opening up to create a gap of 21mm for the fabric strap. As for the strap itself, it features metal-reinforced sizing holes for increased longevity, and both of the strap keepers are made from matte-finished stainless steel to match the wire-style pin buckle.

The dial of the Casio G-Shock COEXIST collection GAB2100CT-5A offers the same fundamental design and layout as what you will find among the standard G-Shock GAB2100 series watches, and it features a pair of centrally-mounted analog hands with a digital screen on the lower right-hand side of its display, plus a function/power reserve indicator placed at 9 o’clock. An assortment of brown and gray hues are used for the various components and text on the dial, although two small splashes of color appear in the form of the red highlight on the function/power reserve indicator hand, and the blue “Tough Solar” text that sits on the opposite side of the dial. Pressing the button located on the upper right-hand side of the case will active a white-colored LED backlight, although the two centrally-mounted hands on the G-Shock COEXIST GAB2100CT-5A are also finished with tan-colored luminous material to help promote low-light visibility. The taupe-colored central section of the dial has a slightly iridescent appearance, and underneath its semi-transparent surface are the solar panels that power the watch.

While it’s easy to overlook the Bluetooth connectivity on the Casio G-Shock COEXIST GAB2100CT-5A among all of its various other functions, this single feature entirely transforms the ownership experience of the watch. In addition to exponentially speeding up the initial configuration process, being able to program the alarm or word time settings from your phone significantly increases the convenience of these features, and G-Shock’s Bluetooth integration also includes a phone-finder feature that enables owners to trigger a sound on their smartphones directly from their watches. Generally speaking, more advanced features come at the cost of battery life, although Casio gets around this issue by making its Bluetooth-equipped movements completely solar-powered. While Casio’s Tough Solar technology is hardly exclusive to the COEXIST series, it does further play into the sustainable resources theme of the collection by eliminating the need for routine battery replacements and reducing the electronic waste that results from single-use power cells.

While I personally enjoy the brown hues and earth-tone colorway of the Casio G-Shock COEXIST GAB2100CT-5A featured here, this sustainability-focused collection also includes another variant of this watch that offers the same overall design but in a more traditional black and gray color profile (GAB2100CT1A5). Additionally, while the fabric strap fitted to this series may not be ideal for those who want something that is quick-drying and can be easily cleaned, it does help create a noticeably different appearance compared to the resin straps that typically accompany G-Shock models. All things considered, my only real complaint with the COEXIST collection GAB2100CT-5A is that its lug adapters significantly increase the lug-to-lug profile of the watch, although this style of adaptor is hardly unique to this particular model, and the brown bio-based resin lug adaptors do ultimately accomplish their goal of allowing the G-Shock’s non-traditional 16mm semi-integrated lugs to be used with a standard 21mm strap.

Casio produces G-Shock watches at an incredibly wide range of different prices, although I personally feel that some of the best value for the money exists within this particular segment, where the models are only slightly more expensive than the brand’s base-level offerings, while still including some of the key game-changing features like solar charging and Bluetooth connectivity. With an official retail price of $170 USD, the Casio G-Shock COEXIST GAB2100CT-5A costs less than most entry-level smartwatches, and it represents a very small premium of only about ten to twenty bucks above what Casio charges for its standard G-Shock GAB2100 series models. Additionally, I’d imagine that this incredibly modest premium is likely due to the lug adaptors and slightly more elaborate strap that is fitted to this particular model, and it seems that Casio is legitimately trying to use the COEXIST collection to promote awareness for renewable materials, rather than trying to use these eco-friendly alternatives as a way to justify a higher price for its watches. For more information on the Casio G-Shock COEXIST GAB2100CT-5A, please visit the brand’s website.