diff --git a/tests/unit/test_system_pin.py b/tests/unit/test_system_pin.py
index 6bdaeeb..fb52be8 100644
--- a/tests/unit/test_system_pin.py
+++ b/tests/unit/test_system_pin.py
@@ -1,6 +1,7 @@
 """Tests for PIN verification on arm/disarm endpoints."""
 
 import pytest
+from unittest.mock import patch
 from vigilar.alerts.pin import hash_pin
 from vigilar.config import VigilarConfig, SecurityConfig
 from vigilar.web.app import create_app
@@ -29,35 +30,55 @@ def app_no_pin():
 
 
 def test_arm_without_pin_set(app_no_pin):
-    with app_no_pin.test_client() as c:
-        rv = c.post("/system/api/arm", json={"mode": "ARMED_AWAY"})
-        assert rv.status_code == 200
-        assert rv.get_json()["ok"] is True
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_no_pin.test_client() as c:
+            rv = c.post("/system/api/arm", json={"mode": "ARMED_AWAY"})
+            assert rv.status_code == 202
+    pub.assert_called_once()
+    payload = pub.call_args.args[1] if len(pub.call_args.args) > 1 else pub.call_args.kwargs["payload"]
+    assert payload["mode"] == "ARMED_AWAY"
+    assert payload["pin"] == ""
 
 
 def test_arm_correct_pin(app_with_pin):
-    with app_with_pin.test_client() as c:
-        rv = c.post("/system/api/arm", json={"mode": "ARMED_AWAY", "pin": "1234"})
-        assert rv.status_code == 200
-        assert rv.get_json()["ok"] is True
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_with_pin.test_client() as c:
+            rv = c.post("/system/api/arm", json={"mode": "ARMED_AWAY", "pin": "1234"})
+            assert rv.status_code == 202
+    pub.assert_called_once()
+    payload = pub.call_args.args[1] if len(pub.call_args.args) > 1 else pub.call_args.kwargs["payload"]
+    assert payload["pin"] == "1234"
 
 
-def test_arm_wrong_pin(app_with_pin):
-    with app_with_pin.test_client() as c:
-        rv = c.post("/system/api/arm", json={"mode": "ARMED_AWAY", "pin": "0000"})
-        assert rv.status_code == 401
+def test_arm_wrong_pin_still_accepted_by_web_fsm_rejects(app_with_pin):
+    """HTTP layer no longer pre-checks the PIN — it forwards to the FSM
+    unconditionally. The FSM verifies and, on mismatch, logs a warning
+    and leaves the state unchanged."""
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_with_pin.test_client() as c:
+            rv = c.post("/system/api/arm", json={"mode": "ARMED_AWAY", "pin": "0000"})
+            assert rv.status_code == 202
+    pub.assert_called_once()
+    payload = pub.call_args.args[1] if len(pub.call_args.args) > 1 else pub.call_args.kwargs["payload"]
+    assert payload["pin"] == "0000"  # forwarded verbatim — FSM will reject
 
 
 def test_disarm_correct_pin(app_with_pin):
-    with app_with_pin.test_client() as c:
-        rv = c.post("/system/api/disarm", json={"pin": "1234"})
-        assert rv.status_code == 200
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_with_pin.test_client() as c:
+            rv = c.post("/system/api/disarm", json={"pin": "1234"})
+            assert rv.status_code == 202
+    pub.assert_called_once()
 
 
-def test_disarm_wrong_pin(app_with_pin):
-    with app_with_pin.test_client() as c:
-        rv = c.post("/system/api/disarm", json={"pin": "9999"})
-        assert rv.status_code == 401
+def test_disarm_wrong_pin_still_accepted_by_web_fsm_rejects(app_with_pin):
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_with_pin.test_client() as c:
+            rv = c.post("/system/api/disarm", json={"pin": "9999"})
+            assert rv.status_code == 202
+    pub.assert_called_once()
+    payload = pub.call_args.args[1] if len(pub.call_args.args) > 1 else pub.call_args.kwargs["payload"]
+    assert payload["pin"] == "9999"  # forwarded verbatim — FSM will reject
 
 
 def test_reset_pin_correct_passphrase(app_with_pin):
@@ -77,3 +98,35 @@ def test_reset_pin_wrong_passphrase(app_with_pin):
             "new_pin": "5678",
         })
         assert rv.status_code == 401
+
+
+def test_arm_publishes_arm_request_on_mqtt(app_with_pin):
+    """POST /system/api/arm must publish a SYSTEM_ARM_REQUEST message
+    carrying the mode, pin, and a 'web' triggered_by tag."""
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_with_pin.test_client() as c:
+            rv = c.post(
+                "/system/api/arm",
+                json={"mode": "ARMED_AWAY", "pin": "1234"},
+            )
+            assert rv.status_code == 202
+            assert rv.get_json()["accepted"] is True
+
+    pub.assert_called_once()
+    call_args = pub.call_args
+    # _publish_arm_request(cfg, payload) — payload is args[1] or kwargs["payload"]
+    payload = call_args.args[1] if len(call_args.args) > 1 else call_args.kwargs["payload"]
+    assert payload["mode"] == "ARMED_AWAY"
+    assert payload["pin"] == "1234"
+    assert payload["triggered_by"] == "web"
+
+
+def test_disarm_publishes_arm_request(app_with_pin):
+    with patch("vigilar.web.blueprints.system._publish_arm_request") as pub:
+        with app_with_pin.test_client() as c:
+            rv = c.post("/system/api/disarm", json={"pin": "1234"})
+            assert rv.status_code == 202
+
+    pub.assert_called_once()
+    payload = pub.call_args.args[1] if len(pub.call_args.args) > 1 else pub.call_args.kwargs["payload"]
+    assert payload["mode"] == "DISARMED"
diff --git a/vigilar/web/blueprints/system.py b/vigilar/web/blueprints/system.py
index 1b39529..884c0c0 100644
--- a/vigilar/web/blueprints/system.py
+++ b/vigilar/web/blueprints/system.py
@@ -54,27 +54,44 @@ def settings_page():
 
 # --- Arm/Disarm ---
 
+def _publish_arm_request(cfg: VigilarConfig, payload: dict) -> None:
+    """Publish an arm/disarm request on MQTT for the event processor to pick up."""
+    from vigilar.bus import MessageBus
+    from vigilar.constants import Topics
+
+    bus = MessageBus(cfg.mqtt, client_id="vigilar-web-arm-request")
+    bus.connect()
+    try:
+        bus.publish(Topics.SYSTEM_ARM_REQUEST, payload)
+    finally:
+        bus.disconnect()
+
+
 @system_bp.route("/api/arm", methods=["POST"])
 def arm_system():
     data = request.get_json() or {}
     mode = data.get("mode", "ARMED_AWAY")
     pin = data.get("pin", "")
-    cfg = _get_cfg()
-    pin_hash = cfg.security.pin_hash
-    if pin_hash and not verify_pin(pin, pin_hash):
-        return jsonify({"error": "Invalid PIN"}), 401
-    return jsonify({"ok": True, "state": mode})
+    payload = {"mode": mode, "pin": pin, "triggered_by": "web"}
+    try:
+        _publish_arm_request(_get_cfg(), payload)
+    except Exception:
+        current_app.logger.exception("Failed to publish arm request")
+        return jsonify({"error": "bus unavailable"}), 503
+    return jsonify({"accepted": True, "mode": mode}), 202
 
 
 @system_bp.route("/api/disarm", methods=["POST"])
 def disarm_system():
     data = request.get_json() or {}
     pin = data.get("pin", "")
-    cfg = _get_cfg()
-    pin_hash = cfg.security.pin_hash
-    if pin_hash and not verify_pin(pin, pin_hash):
-        return jsonify({"error": "Invalid PIN"}), 401
-    return jsonify({"ok": True, "state": "DISARMED"})
+    payload = {"mode": "DISARMED", "pin": pin, "triggered_by": "web"}
+    try:
+        _publish_arm_request(_get_cfg(), payload)
+    except Exception:
+        current_app.logger.exception("Failed to publish arm request")
+        return jsonify({"error": "bus unavailable"}), 503
+    return jsonify({"accepted": True, "mode": "DISARMED"}), 202
 
 
 @system_bp.route("/api/reset-pin", methods=["POST"])