One Kulcar is enough to expel harmful toxins emitted from your car interior in high heat. For four-seater or larger cars, we strongly suggest that you install two Kulcars in each of your car windows for a better cooling effect. Please install Kulcar in the car window that you rarely open. When you use USB to charge your mobile electronic devices, please use it on a sunny day with stable sun light because on a cloudy or gloomy day, it can't provide stable electricity output. Even though Kulcar is efficient at expelling heat and toxins, never leave children or pets in car alone.