Xiaomi has unleashed the Watch S4 Sport as its new wearable for "intensive" pursuits and work-outs, diving included. To this end, it is reinforced with titanium (rotating crown included) as well as sapphire for its 1.43-inch AMOLED display. The S4 Sport also has standalone connectivity and up to 15 days of battery life, yet starts at under $300 in China.