Noise-cancelling headphones were originally created for airline pilots to improve their comfort on long flights, and the first consumer versions were also intended for travellers. The technology, known as active noise-cancellation (ANC), works by using microphones to pick up low-frequency noise and neutralise it before it reaches the ear. The headset generates a sound that's phase-inverted by 180 degrees to the unwanted noise, resulting in the two sounds cancelling each other out.