HTC, the Taiwanese smartphone maker struggling with sliding sales, plans to demonstrate the first of three wearable devices next week in Barcelona, according to a person with direct knowledge of the plans. A smartwatch prototype based on Qualcomm’s Toq device will be previewed to carriers at the Mobile World Congress trade show, with no plans to unveil the device publicly, the person said, asking not to be identified because the details haven’t been released. HTC also is developing a watch using Google’s Now service and an electronic bracelet that plays music, though it may not demonstrate them, the person said. Chairman Cher Wang is counting on new products, more marketing and better customer service to reverse two straight annual declines in revenue as Chinese competitors including Xiaomi Corp. sell smartphones for as low as $100.