diff --git a/src/auth/auth.controller.ts b/src/auth/auth.controller.ts
index ba5837d..8e3494a 100644
--- a/src/auth/auth.controller.ts
+++ b/src/auth/auth.controller.ts
@@ -1,4 +1,5 @@
-import { Controller, Post, Body, Headers, Logger, HttpException } from '@nestjs/common';
+import { Controller, Post, Body, Headers, Req, Logger, HttpException } from '@nestjs/common';
+import type { Request } from 'express';
 import { ConfigService } from '@nestjs/config';
 import axios from 'axios';
 import { OzonetelAgentService } from '../ozonetel/ozonetel-agent.service';
@@ -24,7 +25,7 @@ export class AuthController {
     }
 
     @Post('login')
-    async login(@Body() body: { email: string; password: string }) {
+    async login(@Body() body: { email: string; password: string }, @Req() req: Request) {
         this.logger.log(`Login attempt for ${body.email}`);
 
         try {
@@ -128,13 +129,15 @@ export class AuthController {
                 }
 
                 // Check for duplicate login — strict: one device only
-                const existingSession = await this.sessionService.isSessionLocked(agentConfig.ozonetelAgentId);
+                const clientIp = (req.headers['x-forwarded-for'] as string)?.split(',')[0]?.trim() ?? req.ip ?? 'unknown';
+                const existingSession = await this.sessionService.getSession(agentConfig.ozonetelAgentId);
                 if (existingSession) {
-                    throw new HttpException('You are already logged in on another device. Please log out there first.', 409);
+                    this.logger.warn(`Duplicate login blocked for ${body.email} — session held by IP ${existingSession.ip} since ${existingSession.lockedAt}`);
+                    throw new HttpException(`You are already logged in from another device (${existingSession.ip}). Please log out there first.`, 409);
                 }
 
-                // Lock session in Redis
-                await this.sessionService.lockSession(agentConfig.ozonetelAgentId, memberId);
+                // Lock session in Redis with IP
+                await this.sessionService.lockSession(agentConfig.ozonetelAgentId, memberId, clientIp);
 
                 // Login to Ozonetel with agent-specific credentials
                 const ozAgentPassword = process.env.OZONETEL_AGENT_PASSWORD ?? 'Test123$';
diff --git a/src/auth/session.service.ts b/src/auth/session.service.ts
index f1aa198..b695002 100644
--- a/src/auth/session.service.ts
+++ b/src/auth/session.service.ts
@@ -22,12 +22,25 @@ export class SessionService implements OnModuleInit {
         return `agent:session:${agentId}`;
     }
 
-    async lockSession(agentId: string, memberId: string): Promise<void> {
-        await this.redis.set(this.key(agentId), memberId, 'EX', SESSION_TTL);
+    async lockSession(agentId: string, memberId: string, ip?: string): Promise<void> {
+        const value = JSON.stringify({ memberId, ip: ip ?? 'unknown', lockedAt: new Date().toISOString() });
+        await this.redis.set(this.key(agentId), value, 'EX', SESSION_TTL);
+    }
+
+    async getSession(agentId: string): Promise<{ memberId: string; ip: string; lockedAt: string } | null> {
+        const raw = await this.redis.get(this.key(agentId));
+        if (!raw) return null;
+        try {
+            return JSON.parse(raw);
+        } catch {
+            // Legacy format — just memberId string
+            return { memberId: raw, ip: 'unknown', lockedAt: 'unknown' };
+        }
     }
 
     async isSessionLocked(agentId: string): Promise<string | null> {
-        return this.redis.get(this.key(agentId));
+        const session = await this.getSession(agentId);
+        return session ? session.memberId : null;
     }
 
     async refreshSession(agentId: string): Promise<void> {