When we first saw the first Casio G-Shock Bluetooth-compatible watch - the GB-6900 - there were a couple of things that were different. First, it was connected to an Android smartphone. And second, it only came in black with a white (grey) face.Now, having been released in the US recently and due to come to the UK in 2013, there's \u00a0a swathe of other colour schemes, all of which appeared on the Casio stand at CES 2013 in Las Vegas, and compatible only with the iPhone 4S and iPhone 5 at present.The Casio G-Shock GB-6900AA is available for $180 in the States (around \u00a3111) and now comes in gloss black with a silver and black face, gloss blue with a silver and blue face, gloss brown with a silver and black face, and gloss white with a silver and white face.They each carry the same feature set as the original version released in Japan in 2011. The Bluetooth connectivity allows the watch to inform its wearer of inbound email and text messages, including the sender name. And it can display the name of a song currently playing on an iDevice.But the feature we've been most impressed by each time we've seen a Casio G-Shock Bluetooth watch is that it will tell you when you've strayed too far from your phone, ensuring that you don't leave it behind.Because the profile is Bluetooth v4.0 it is also power efficient, even when it is constantly connected. And a time synchronisation function means it will always display the same time as your iPhone.The reason it is currently iOS compatible only is purely because of the free application needed to drive the watch's features. The Android version is yet to be approved, but Casio tells us that it is in the pipeline for the coming months.Hopefully, we'll see the GB-6900 hit the UK soon, along with the newer Casio G-Shock GB-5600A we also played with at CES.