Active Noise Cancellation: Hybrid 3 layer active noise cancellation. 1. Outward-facing microphone detects external sounds and counter with equal anti-noise to reduce the environmental noise up to more than 35dB. 2. Inward-facing microphone listens inside ear canal to pick up internal sounds and produce anti-noise again to twice cancel the left noise. 3. Ear caps prevent 90% noise going to ear canal. Transparency Mode: You can hear what you want to hear, which lets outside sound in so you can hear and interact with the world around you. You can clearly hear the announcement of the airline or subway and what is saying around you without taking off the headphones. Optical Sensors Technology & One-step Pairing Charge on the Go: TOZO NC2 earbuds can last for over 10 hours' playtime from a single charge and total 42 hours with the compact charging case. IPX6 waterproof can prevent from the damage of the splash by sweat and raindrops.