diff --git a/pico-dashboard/alarms/alarm_definitions.py b/pico-dashboard/alarms/alarm_definitions.py
index e69de29..943896e 100644
--- a/pico-dashboard/alarms/alarm_definitions.py
+++ b/pico-dashboard/alarms/alarm_definitions.py
@@ -0,0 +1,13 @@
+BATTERY_SOC_LOW = "battery_soc_low"
+BATTERY_VOLTAGE_LOW = "battery_voltage_low"
+FRIDGE_ZONE_1_HIGH = "fridge_zone_1_high"
+FRIDGE_ZONE_2_HIGH = "fridge_zone_2_high"
+SENSOR_FAILURE = "sensor_failure"
+COMMUNICATION_LOST = "communication_lost"
+
+
+DEFAULT_THRESHOLDS = {
+    "battery_soc_low": 20,
+    "battery_voltage_low": 12.0,
+    "fridge_temp_high": 40.0,
+}
diff --git a/pico-dashboard/alarms/alarm_manager.py b/pico-dashboard/alarms/alarm_manager.py
index e69de29..2b3e10d 100644
--- a/pico-dashboard/alarms/alarm_manager.py
+++ b/pico-dashboard/alarms/alarm_manager.py
@@ -0,0 +1,44 @@
+from .alarm_definitions import (
+    BATTERY_SOC_LOW,
+    BATTERY_VOLTAGE_LOW,
+    FRIDGE_ZONE_1_HIGH,
+    FRIDGE_ZONE_2_HIGH,
+    SENSOR_FAILURE,
+    COMMUNICATION_LOST,
+    DEFAULT_THRESHOLDS,
+)
+
+
+class AlarmManager:
+    def __init__(self, thresholds=None):
+        self.thresholds = dict(DEFAULT_THRESHOLDS)
+        if thresholds:
+            self.thresholds.update(thresholds)
+
+    def evaluate(self, state):
+        alarms = []
+
+        soc = state.battery.get("soc")
+        if soc is not None and soc < self.thresholds["battery_soc_low"]:
+            alarms.append(BATTERY_SOC_LOW)
+
+        voltage = state.battery.get("voltage")
+        if voltage is not None and voltage < self.thresholds["battery_voltage_low"]:
+            alarms.append(BATTERY_VOLTAGE_LOW)
+
+        z1 = state.temps.get("fridge_zone_1")
+        if z1 is not None and z1 > self.thresholds["fridge_temp_high"]:
+            alarms.append(FRIDGE_ZONE_1_HIGH)
+
+        z2 = state.temps.get("fridge_zone_2")
+        if z2 is not None and z2 > self.thresholds["fridge_temp_high"]:
+            alarms.append(FRIDGE_ZONE_2_HIGH)
+
+        if not state.network.get("uart_connected", False):
+            alarms.append(COMMUNICATION_LOST)
+
+        for sensor_name, online in state.sensor_health.items():
+            if not online:
+                alarms.append(f"{SENSOR_FAILURE}:{sensor_name}")
+
+        return alarms
diff --git a/pico-dashboard/comms/protocol.py b/pico-dashboard/comms/protocol.py
index e69de29..ec32f69 100644
--- a/pico-dashboard/comms/protocol.py
+++ b/pico-dashboard/comms/protocol.py
@@ -0,0 +1,35 @@
+STATUS_REQUEST = "status_request"
+STATUS_RESPONSE = "status_response"
+SET_RELAY = "set_relay"
+RELAY_RESPONSE = "relay_response"
+ERROR = "error"
+
+
+VALID_RELAYS = {"starlink", "fridge"}
+
+
+def make_status_request():
+    return {"type": STATUS_REQUEST}
+
+
+def make_set_relay(relay, enabled):
+    if relay not in VALID_RELAYS:
+        raise ValueError(f"Invalid relay: {relay}")
+
+    return {
+        "type": SET_RELAY,
+        "relay": relay,
+        "enabled": bool(enabled),
+    }
+
+
+def is_status_response(message):
+    return message.get("type") == STATUS_RESPONSE
+
+
+def is_relay_response(message):
+    return message.get("type") == RELAY_RESPONSE
+
+
+def is_error(message):
+    return message.get("type") == ERROR
diff --git a/pico-dashboard/state/app_state.py b/pico-dashboard/state/app_state.py
index e69de29..e19a05d 100644
--- a/pico-dashboard/state/app_state.py
+++ b/pico-dashboard/state/app_state.py
@@ -0,0 +1,61 @@
+class AppState:
+    def __init__(self):
+        self.battery = {
+            "soc": None,
+            "voltage": None,
+            "current": None,
+            "remaining_ah": None,
+            "runtime_hours": None,
+            "temperature_f": None,
+        }
+
+        self.temps = {
+            "fridge_zone_1": None,
+            "fridge_zone_2": None,
+            "rear_seat": None,
+            "outside": None,
+        }
+
+        self.sensor_health = {
+            "fridge_zone_1": False,
+            "fridge_zone_2": False,
+            "rear_seat": False,
+            "outside": False,
+        }
+
+        self.relays = {
+            "starlink": False,
+            "fridge": False,
+        }
+
+        self.vehicle = {
+            "ignition_on": False,
+        }
+
+        self.network = {
+            "uart_connected": False,
+            "wifi_enabled": False,
+        }
+
+        self.last_error = None
+        self.last_status_timestamp = None
+
+    def update_from_status(self, message):
+        self.last_status_timestamp = message.get("timestamp")
+
+        self.battery.update(message.get("battery", {}))
+        self.temps.update(message.get("temps", {}))
+        self.sensor_health.update(message.get("sensor_health", {}))
+        self.relays.update(message.get("relays", {}))
+        self.vehicle.update(message.get("vehicle", {}))
+        self.network.update(message.get("network", {}))
+
+    def update_from_relay_response(self, message):
+        relay = message.get("relay")
+        enabled = message.get("enabled")
+
+        if relay in self.relays and enabled is not None:
+            self.relays[relay] = bool(enabled)
+
+    def set_error(self, message):
+        self.last_error = message
diff --git a/pico-dashboard/ui/screen_manager.py b/pico-dashboard/ui/screen_manager.py
index e69de29..d6110e4 100644
--- a/pico-dashboard/ui/screen_manager.py
+++ b/pico-dashboard/ui/screen_manager.py
@@ -0,0 +1,21 @@
+class ScreenManager:
+    VALID_SCREENS = ("dashboard", "battery", "temps", "power", "system")
+
+    def __init__(self):
+        self.current_screen = "dashboard"
+
+    def go_to(self, screen_name):
+        if screen_name not in self.VALID_SCREENS:
+            raise ValueError(f"Invalid screen: {screen_name}")
+
+        self.current_screen = screen_name
+
+    def next_screen(self):
+        current_index = self.VALID_SCREENS.index(self.current_screen)
+        next_index = (current_index + 1) % len(self.VALID_SCREENS)
+        self.current_screen = self.VALID_SCREENS[next_index]
+
+    def previous_screen(self):
+        current_index = self.VALID_SCREENS.index(self.current_screen)
+        previous_index = (current_index - 1) % len(self.VALID_SCREENS)
+        self.current_screen = self.VALID_SCREENS[previous_index]