Smart watches seem to be one of the big trends at this year's CES trade show, and one of the first out of the blocks with a Bluetooth v4.0 timepiece was Casio, with its Casio G-Shock GB-6900 shown at last year's event and released a few months ago in the US.Now it has added a second device to the line-up, one that isn't being exhibited on the show floor. However, Pocket-lint managed to get a sneak peek and brief play with the Casio G-Shock GB-5600A.It looks less ostentatious than the model currently available - more like a classic digital watch from the early Nineties than a traditional G-Shock. It has the same sort of capabilities though, hooking up to an iPhone 5 or 4S using Bluetooth and syncing with the same free app as the 6900.Although we didn't get to see all of the functions at work, its older sibling can show caller ID, alerts you to incoming text messages and emails, and scrolls the name of the song currently playing on your iDevice.One of the features we were most impressed with last year was the watch's ability to buzz when it gets too far away from your phone - essentially giving you a reminder that you've left it behind.We've been told that the GB-5600A will do basically the same as the chunkier version, and will retail for around the same price too.According to Casio, it will be out in the US around summer time, and will cost roughly $180. Unfortunately, UK availability details are yet to be revealed. It will work only with iPhone at present - because of the app support - but an Android app is in the pipeline for release later in the year.