There are a few Bluetooth watches available already, with varying levels of usefulness, but Casio's forthcoming attempt is different. For starters, it's a G-Shock, so is already worth the attention, and secondarily it uses the low energy Bluetooth 4.0, so is power friendly and, therefore, can run for up to 2 years on a single battery.But we jump ahead of ourselves here, the Casio G-Shock GB-6900 looks, for all intents and purposes, like a normal G-Shock. It only comes in black, but presents the same bold and chunky plastic body that is popular amongst rap stars and, you know, the kids. And it tells the time.The Bluetooth shenanigans add several other features to the mix, including email and caller ID and alerts. When hooked up to a compatible smartphone or other device, the watch informs you when you receive a call by vibrating and showing the name of the caller in a small, dedicated panel in the top left of the fascia. It will do the same with emails too, displaying the name of the sender.Additionally, although not so usefully in our opinion, it will scroll the name of the song you're listening to on your device.But, funnily enough, our favourite feature, as demonstrated to us at CES in Las Vegas, was the ability for the watch to warn you if you get too far away from the device it's paired with. For example, if you go more than 2 metres away from your smartphone, it will beep, ensuring that you never accidentally leave your phone or tablet behind (the Bluetooth range is expected to be around 2 metres anyway, so it's an easy feature to implement).It is also future-proofed for other applications, as more Bluetooth 4.0-compatible devices are devised. Take the medical profession for example, it could sync with heart rate or blood pressure monitors. Or your car in order to show, er, car things. A world of possibilities, we're sure you'll agree.Sadly though, this is also the reason we may not see the GB-6900 in the UK anytime soon; at present there are few devices that are Bluetooth 4.0-enabled, with the smartphones that are compatible currently only being available in Japan - hence a Japanese release is scheduled for this coming March at 18,000 Yen (around \u00a3150).According to Casio, the US and UK are likely to have to wait until the end of this year at best, more likely 2013. Hopefully by then though, the company will have come up with some new colour schemes too.