diff --git a/serial_heartbeat.py b/serial_heartbeat.py
index 8cc14eb..911948c 100644
--- a/serial_heartbeat.py
+++ b/serial_heartbeat.py
@@ -7,6 +7,8 @@ import argparse
 import json
 import logging
 import os
+import socket
+import subprocess
 import sys
 import time
 from typing import Generator, Optional
@@ -121,8 +123,52 @@ def iter_json_objects(port: serial.Serial, systemd: Optional[SystemdIntegration]
                 yield payload
 
 
+def vpn_status(interface: str = "tun0") -> int:
+    """Return 1 if the interface exists (and is up when operstate is available), else 0."""
+    try:
+        if interface in {name for _, name in socket.if_nameindex()}:
+            operstate_path = f"/sys/class/net/{interface}/operstate"
+            carrier_path = f"/sys/class/net/{interface}/carrier"
+            if os.path.exists(operstate_path):
+                try:
+                    with open(operstate_path, "r", encoding="utf-8") as fh:
+                        state = fh.read().strip().lower()
+                        if state == "up":
+                            return 1
+                        if state == "down":
+                            return 0
+                        # Some tun devices report "unknown"; fall back to carrier/exists.
+                except OSError:
+                    pass
+            if os.path.exists(carrier_path):
+                try:
+                    with open(carrier_path, "r", encoding="utf-8") as fh:
+                        return 1 if fh.read().strip() == "1" else 0
+                except OSError:
+                    pass
+            return 1
+    except OSError:
+        logging.debug("Unable to determine VPN interface state.", exc_info=True)
+    return 0
+
+
+def app_status(service: str = "watcher_application.service") -> int:
+    """Return 1 if the systemd service is active, else 0."""
+    try:
+        result = subprocess.run(
+            ["systemctl", "is-active", "--quiet", service],
+            check=False,
+            stdout=subprocess.DEVNULL,
+            stderr=subprocess.DEVNULL,
+        )
+        return 1 if result.returncode == 0 else 0
+    except (FileNotFoundError, OSError):
+        logging.debug("Unable to query systemd service state for %s.", service, exc_info=True)
+    return 0
+
+
 def relay_heartbeat(port_name: str, baudrate: int, systemd: Optional[SystemdIntegration] = None) -> None:
-    """Read heartbeats from ``port_name`` and reply with {"hb": 2}."""
+    """Read heartbeats from ``port_name`` and reply with {"hb": 2, "VPN": <0|1>, "APP": <0|1>}."""
     try:
         if systemd:
             systemd.status(f"Opening serial port {port_name} @ {baudrate} baud")
@@ -132,10 +178,12 @@ def relay_heartbeat(port_name: str, baudrate: int, systemd: Optional[SystemdInte
                 systemd.ready(f"Listening on {port_name} @ {baudrate} baud")
             for message in iter_json_objects(ser, systemd):
                 hb_value = message.get("hb")
-                logging.debug("Received payload %s", message)
+                cmd_value = message.get("cmd")
+                logging.info("Received payload %s", message)
 
-                if hb_value == 1:
-                    ack = json.dumps({"hb": 2}, separators=(",", ":")).encode("utf-8") + b"\n"
+                if hb_value == 1 or cmd_value == "status":
+                    ack_payload = {"hb": 2, "VPN": vpn_status(), "APP": app_status()}
+                    ack = json.dumps(ack_payload, separators=(",", ":")).encode("utf-8") + b"\n"
                     ser.write(ack)
                     ser.flush()
                     logging.info("Sent reply %s", ack.strip())