Hi @rkao
I can’t provide exact information without knowing what specific models you’ve purchased. However, I can provide some general information. Our newer models, the Zen, Touch, and Flex, will display LEDs that change color based upon air quality. Those colors are based on the US EPA PM2.5 AQI.
Secondly, as long as a device is plugged in, it should shine a static red LED inside the device housing. This is an indicator that the device is receiving proper power. If the LED is blinking or not visible, it means the device is not receiving enough, or no, power.
Lastly, you may see a blinking blue LED. The LED will flicker differently depending on the status of the SD card. More information is available in the linked article.