Just opening windows and doors before hitting the sack can help you get a good night's sleep according to a recent study. The research found that opening windows or doors before going to bed can reduce carbon dioxide levels in bedrooms and improve sleep quality. The participants' subjective assessment of their sleep depth which was obtained through questionnaires correlated with carbon dioxide levels. Objectively measured sleep efficiency and number of awakenings which were assessed through senses worn during sleep also correlated with carbon dioxide levels. Lower carbon dioxide levels implied better sleep depth sleep efficiency and lesser number of awakenings.