jǐng​jiè​xiàn

alert level

警戒线 (警戒線) jǐng​jiè​xiàn
alert level noun
a threshold or warning line, such as for water levels or security threats, indicating a state of danger

The river level has exceeded the safety warning line.

cordon noun
a physical line or boundary set up by police or security forces to restrict access to an area

Police cordoned off the scene of the accident.

Frequency

Movie subtitles
2.15 per million appears in 1% of films
Written text
3.12 per million

Sources

Definitions
CC-CEDICT