Sometimes keeping all your windows closed can be a bad thing. We have air quality sensors all over our home. Some are Eve Room devices and some are built into our Air Purifiers with carbon dioxide sensors. Often times when levels spike and we’re not doing anything to cause it like cooking food then it’s a good sign to open the window. That always brings the levels down. When the carbon dioxide sensor registers high values it’s typically in our bedroom while we’re sleeping. I definitely notice that we get headaches and poor sleep when carbon dioxide is elevated.