diff --git a/src/rtmt/rtmt.ts b/src/rtmt/rtmt.ts
index aa8ccdf..238cad0 100644
--- a/src/rtmt/rtmt.ts
+++ b/src/rtmt/rtmt.ts
@@ -1,8 +1,10 @@
 export type Bytes = Buffer
 export type OnMessage = (clientID: string, message: Object) => any
+export type OnClientConnectionChange = (clientID: string, isOnline : boolean) => any
 
 export interface RTMT {
     sendMessage: (clientID: string, channel: string, message: Object) => any;
     listenMessage: (channel: string, callback: OnMessage) => any;
     isClientOnline(clientID: string): boolean;
+    listenOnClientConnectionChange(onUserConnectionChange: OnClientConnectionChange): void;
 }
\ No newline at end of file
diff --git a/src/rtmt/rtmt_websocket.ts b/src/rtmt/rtmt_websocket.ts
index 45d8529..5f63494 100644
--- a/src/rtmt/rtmt_websocket.ts
+++ b/src/rtmt/rtmt_websocket.ts
@@ -1,5 +1,5 @@
 import { decode, encode } from "./encode_decode_message"
-import { Bytes, OnMessage, RTMT } from "./rtmt"
+import { Bytes, OnClientConnectionChange, OnMessage, RTMT } from "./rtmt"
 
 import WebSocket from "ws"
 import * as http from 'http';
@@ -17,6 +17,8 @@ export class RTMTWS implements RTMT {
 
     private pingInterval?: NodeJS.Timeout = undefined;
 
+    onUserConnectionChange?: OnClientConnectionChange;
+
     constructor() {
         this.messageChannels = new Map<String, OnMessage>()
         this.wsServer = null
@@ -32,6 +34,7 @@ export class RTMTWS implements RTMT {
             const regexResult = req.url.split(RegExp("\/\?userKey="));
             const clientID = regexResult[1]
             this.clients.set(clientID, ws)
+            this.onUserConnectionChange?.(clientID, true);
             ws.on("message", (messageBytes: string) => {
                 this.onWebSocketMessage(clientID, messageBytes)
             })
@@ -39,6 +42,7 @@ export class RTMTWS implements RTMT {
             ws.on("close", (code: number, reason: string) => {
                 console.log("WS Closed! code : " + code + " reason : " + reason);
                 this.clients.delete(clientID)
+                this.onUserConnectionChange?.(clientID, false);
             })
 
             ws.on("error", (err: Error) => {
@@ -130,4 +134,8 @@ export class RTMTWS implements RTMT {
     isClientOnline(clientID: string): boolean {
         return this.clients.has(clientID);
     }
+
+    listenOnClientConnectionChange(onUserConnectionChange: OnClientConnectionChange) {
+        this.onUserConnectionChange = onUserConnectionChange;
+    }
 }
\ No newline at end of file