警戒线 (jǐngjièxiàn): police cordon; security perimeter

Measure Word

一条警戒线 tiáo

Jǐngchá zài shìgù xiànchǎng lāqǐ le jǐngjièxiàn.

The police set up a cordon at the accident scene.

Qǐng bùyào yuèguò jǐngjièxiàn.

Please do not cross the security line.

警 jǐng

戒 jiè

线 xiàn