Stainless steel link strap and an interchangeable leather strap. Compatible with Android and IOS. 42mm diameter, the most classic watch size. Sapphire Crystal screen, Always-On Screen & Voice Interaction - see important details at a glance, without touching your watch, such as social media notifications, all your messages, who's calling and turn-by-turn navigation instruction. Fitness Tracking and Heart Rate Monitor - a high-accuracy motion sensor keeps track of your activity and knows when you’re walking, running or climbing.