To understand why a tight fit is important for smartwatch data capture, first, it's important to understand how the smartwatch sensors work.

You may see your smartwatch glowing green around your wrist as you exercise or monitor your heart rate. That green light is actually essential in recording workout data. To continuously monitor your heart rate, a smartwatch emits green light onto your wrist.

Red and green are complementary colors, and as your heart pumps blood during exercise, the green light absorbs the red blood. Between heartbeats, blood absorbs less green light, so more green light bounces back into the watch.