Commercial airline British Airways invented a “happiness blanket” linked with sensors that measure brainwaves, which it then had passengers wear during a flight. The blanket is outfitted with fiberoptics that “visually indicate what the wearer is feeling” based on the user’s brainwave activity, according to British Airways, turning red when stressed and blue when calm.

“Most importantly, we discovered the unwavering sense of well-being created by being able to sync into deep, undisrupted sleep,” says a British Airways video, showing the blankets turning blue as passengers drift into sleep.

Many airlines have made improvements in their in-flight sleep environments in recent months, including Delta, Etihad Airways, and Virgin Atlantic.