警戒 (jǐng jiè) means 'to warn, to alert' in an official or authoritative context, such as a government or police issuing a public warning. It differs from 警告 (jǐng gào), which is a more direct personal admonition or reprimand, and from 警示 (jǐng shì), which emphasizes signaling a danger or lesson. 警戒 also carries a sense of 'being on guard' (e.g., 警戒状态).