If you’re often blinded by the sunlight that shines through your car windshield, self-tinting windows offer welcome relief. But those already on the market take more than 20 minutes to go from clear to opaque, and they become less dark over time. Now, researchers have developed a new, cheaper smart window that dims in less than a minute, and can be switched on and off more than 5000 times without degrading. The prototypes are glass plates coated with a thin film of an alloy known as indium tin oxide, and outlined with a liquid mixture of copper and another metal—either lead or silver. When charged with electrical current, the mixture of dark metals spreads over the glass surface, blocking up to 95% of the surrounding light depending on your preferences, the team reports today in Joule. When the window goes back to transparent, a process that also happens within seconds, about 80% of the light can shine through it. By optimizing the lighting in cars and houses, smart windows can help reduce heating and cooling costs and eliminate the need for blinds, the scientists say, but more work needs to be done to produce larger windows that can be commercialized.