/sɚˈveɪ.ləns/
the careful watching of a person or place, especially by the police or army, because of a crime that has happened or is expected:
The police have kept the nightclub under surveillance because of suspected illegal drug activity.
More banks are now installing surveillance cameras.
the act of carefully watching a person suspected of a crime or a place where a crime may be committed （对犯罪嫌疑人或可能发生犯罪的地方的）监视 SYN observation
The police are keeping the suspects under constant surveillance.
警方正对嫌疑人实施不间断监视。
surveillance cameras/equipment
监视摄像机／设备