2 sentences for 便衣 (biàn​yī)

1. 他今天穿着便衣，没穿警服。

   tā jīn​tiān chuān​zhe biàn​yī, méi chuān jǐng​fú.

   He is wearing plain clothes today instead of his police uniform.

   Source: Dong Chinese Dictionary

2. 几名便衣混在人群中执行任务。

   jǐ míng biàn​yī hùn zài rén​qún zhōng zhí​xíng rèn​wu.

   Several plainclothes officers mingled with the crowd to carry out their mission.

   Source: Dong Chinese Dictionary