diff --git a/check_errors.py b/check_errors.py
new file mode 100755
index 0000000..a7928c8
--- /dev/null
+++ b/check_errors.py
@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+"""Check API errors in the last hour and send Slack alert if any found."""
+
+import os
+import sys
+from datetime import datetime, timedelta
+
+sys.path.insert(0, os.path.dirname(__file__))
+
+import slack_notifier
+
+
+LOG_FILES = [
+    "trading.log",
+    "sync_cost_basis.log",
+    "cron.log",
+]
+
+LOOKBACK_MINUTES = 60
+
+
+def collect_recent_errors() -> list[str]:
+    since = datetime.now() - timedelta(minutes=LOOKBACK_MINUTES)
+    since_str = since.strftime("%Y-%m-%d %H:%M")
+    errors = []
+
+    for logfile in LOG_FILES:
+        path = os.path.join(os.path.dirname(__file__), logfile)
+        if not os.path.exists(path):
+            continue
+        with open(path) as f:
+            for line in f:
+                if "[ERROR]" not in line:
+                    continue
+                # Only compare lines that start with a timestamp
+                if not line[:4].isdigit():
+                    continue
+                if line[:16] >= since_str:
+                    errors.append(line.rstrip())
+
+    return errors
+
+
+def main():
+    errors = collect_recent_errors()
+    if not errors:
+        return
+
+    # Deduplicate and limit
+    unique = list(dict.fromkeys(errors))
+    display = unique[:20]
+    remaining = len(unique) - len(display)
+
+    lines = [
+        "<!channel>",
+        f"⚠️ *API 錯誤警報* (最近 {LOOKBACK_MINUTES} 分鐘，共 {len(unique)} 筆)",
+        "",
+    ]
+    for e in display:
+        lines.append(f"• `{e[:200]}`")
+    if remaining > 0:
+        lines.append(f"\n...另有 {remaining} 筆錯誤")
+
+    slack_notifier._send({"text": "\n".join(lines)})
+
+
+if __name__ == "__main__":
+    main()
diff --git a/setup.sh b/setup.sh
index 5c87f2e..22ab54e 100755
--- a/setup.sh
+++ b/setup.sh
@@ -118,6 +118,7 @@ echo "[6/6] Setting up crontab..."
 
 CRON_MAIN="*/5 * * * * sleep 30 && cd $PROJECT_DIR && /usr/bin/python3 main.py >> cron.log 2>&1"
 CRON_SYNC="2,32 * * * * cd $PROJECT_DIR && /usr/bin/python3 sync_cost_basis.py >> sync_cost_basis_cron.log 2>&1"
+CRON_CHECK="*/5 * * * * cd $PROJECT_DIR && /usr/bin/python3 check_errors.py 2>&1"
 CRON_ENV="PATH=$HOME/.local/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
 CRON_PYPATH="PYTHONPATH=$HOME/.local/lib/python3.12/site-packages"
 
@@ -136,6 +137,7 @@ $CRON_PYPATH
 
 $CRON_MAIN
 $CRON_SYNC
+$CRON_CHECK
 CRONTAB
     ) | crontab -
     echo "  crontab installed ✓"
@@ -157,5 +159,6 @@ else
 fi
 echo ""
 echo "Crontab 排程："
-echo "  main.py:           每 5 分鐘（延遲 30 秒）"
-echo "  sync_cost_basis.py: 每小時 :02 和 :32"
+echo "  main.py:            每 5 分鐘（延遲 30 秒）"
+echo "  sync_cost_basis.py:  每小時 :02 和 :32"
+echo "  check_errors.py:     每 5 分鐘（有錯才 Slack @channel）"