This Air purifier will work once it is connected with a USB power source and there is no need to press it to turn on. You can long-press to turn it off and turn it on again. Once you connect it with a USB power source, it works with default Auto-Mode which will automatically change the fan speed according to the air quality. Then you can short press once again to change it to Strong-Mode (the LED flashes quickly) which has the best purifying ability and airflow. If you short press again from Strong-mode, the Air purifier will go into the Silent-Mode (the LED flashes slowly)