1 sentence

1. 当空气质量差时，室内传感器显示为红灯。

   dāng kōng​qì​zhì​liàng chà shí, shì​nèi chuán​gǎn​qì xiǎn​shì wéi hóng​dēng.

   When the air quality is poor, the indoor sensor shows a red light.

   Source: CCMatrix