diff --git a/config/runtime.exs b/config/runtime.exs
index a7f13ed5..32daa9fe 100644
--- a/config/runtime.exs
+++ b/config/runtime.exs
@@ -236,9 +236,11 @@ if config_env() == :prod do
       # for details about using IPv6 vs IPv4 and loopback vs public addresses.
       ip: {0, 0, 0, 0, 0, 0, 0, 0},
       # Bandit uses ThousandIsland for connection management
-      # Timeout for reading client data before closing the connection (30 seconds)
+      # Timeout for reading client data before closing the connection.
+      # Set high enough to accommodate long-lived WebSocket connections
+      # (agents send Phoenix transport heartbeats every 25s).
       thousand_island_options: [
-        read_timeout: 30_000
+        read_timeout: 120_000
       ]
     ],
     secret_key_base: secret_key_base
diff --git a/lib/towerops/agents.ex b/lib/towerops/agents.ex
index 3b904e86..0f8d57b4 100644
--- a/lib/towerops/agents.ex
+++ b/lib/towerops/agents.ex
@@ -616,6 +616,43 @@ defmodule Towerops.Agents do
     end
   end
 
+  @doc """
+  Checks if a device should be polled by Phoenix directly.
+
+  Returns false if the device is assigned to a non-cloud-poller agent
+  (i.e., a customer/local agent). Phoenix should never poll devices that
+  are assigned to local agents - those devices should only be polled by
+  their assigned agent.
+
+  Returns true if:
+  - No agent is assigned to the device
+  - The device is assigned to a cloud poller (Phoenix-hosted agent)
+
+  ## Examples
+
+      iex> should_phoenix_poll_device?(device_with_local_agent)
+      false
+
+      iex> should_phoenix_poll_device?(device_with_cloud_poller)
+      true
+
+      iex> should_phoenix_poll_device?(device_no_agent)
+      true
+
+  """
+  def should_phoenix_poll_device?(%Device{} = device) do
+    case get_effective_agent_token(device) do
+      nil ->
+        # No agent assigned - Phoenix can poll
+        true
+
+      agent_token_id ->
+        # Check if the agent is a cloud poller
+        agent_token = get_agent_token!(agent_token_id)
+        agent_token.is_cloud_poller
+    end
+  end
+
   ## PubSub notifications
 
   @doc """
diff --git a/lib/towerops/workers/device_monitor_worker.ex b/lib/towerops/workers/device_monitor_worker.ex
index cbf3cf05..68371b99 100644
--- a/lib/towerops/workers/device_monitor_worker.ex
+++ b/lib/towerops/workers/device_monitor_worker.ex
@@ -14,6 +14,7 @@ defmodule Towerops.Workers.DeviceMonitorWorker do
       states: [:available, :scheduled, :executing, :retryable]
     ]
 
+  alias Towerops.Agents
   alias Towerops.Alerts
   alias Towerops.Devices
   alias Towerops.Monitoring
@@ -34,22 +35,33 @@ defmodule Towerops.Workers.DeviceMonitorWorker do
         :ok
 
       device ->
-        _ =
-          if device.monitoring_enabled do
-            perform_check(device)
-          end
+        maybe_perform_check(device)
+        schedule_next_check_with_error_handling(device_id)
+        :ok
+    end
+  end
 
-        # Schedule next check
-        case schedule_next_check(device_id) do
-          {:ok, _job} ->
-            :ok
+  defp maybe_perform_check(device) do
+    cond do
+      not device.monitoring_enabled ->
+        :ok
 
-          {:error, changeset} ->
-            Logger.error("Failed to schedule next monitoring check for device #{device_id}: #{inspect(changeset.errors)}")
+      not Agents.should_phoenix_poll_device?(device) ->
+        Logger.debug("Skipping Phoenix monitoring for device #{device.name} - assigned to non-cloud-poller agent")
+        :ok
 
-            :ok
-        end
+      true ->
+        perform_check(device)
+    end
+  end
 
+  defp schedule_next_check_with_error_handling(device_id) do
+    case schedule_next_check(device_id) do
+      {:ok, _job} ->
+        :ok
+
+      {:error, changeset} ->
+        Logger.error("Failed to schedule next monitoring check for device #{device_id}: #{inspect(changeset.errors)}")
         :ok
     end
   end
diff --git a/lib/towerops/workers/device_poller_worker.ex b/lib/towerops/workers/device_poller_worker.ex
index 1a4f99e4..b007b6c2 100644
--- a/lib/towerops/workers/device_poller_worker.ex
+++ b/lib/towerops/workers/device_poller_worker.ex
@@ -20,6 +20,7 @@ defmodule Towerops.Workers.DevicePollerWorker do
       states: [:available, :scheduled, :executing, :retryable]
     ]
 
+  alias Towerops.Agents
   alias Towerops.Devices
   alias Towerops.Snmp
   alias Towerops.Snmp.ArpDiscovery
@@ -40,23 +41,35 @@ defmodule Towerops.Workers.DevicePollerWorker do
         :ok
 
       device ->
-        if device.snmp_enabled do
-          poll_device(device)
-        end
+        maybe_poll_device(device)
+        schedule_next_poll_with_error_handling(device_id, device)
+        :ok
+    end
+  end
 
-        # Schedule next poll
-        poll_interval = get_poll_interval(device)
+  defp maybe_poll_device(device) do
+    cond do
+      not device.snmp_enabled ->
+        :ok
 
-        case schedule_next_poll(device_id, poll_interval) do
-          {:ok, _job} ->
-            :ok
+      not Agents.should_phoenix_poll_device?(device) ->
+        Logger.debug("Skipping Phoenix poll for device #{device.name} - assigned to non-cloud-poller agent")
+        :ok
 
-          {:error, changeset} ->
-            Logger.error("Failed to schedule next poll for device #{device_id}: #{inspect(changeset.errors)}")
+      true ->
+        poll_device(device)
+    end
+  end
 
-            :ok
-        end
+  defp schedule_next_poll_with_error_handling(device_id, device) do
+    poll_interval = get_poll_interval(device)
 
+    case schedule_next_poll(device_id, poll_interval) do
+      {:ok, _job} ->
+        :ok
+
+      {:error, changeset} ->
+        Logger.error("Failed to schedule next poll for device #{device_id}: #{inspect(changeset.errors)}")
         :ok
     end
   end
diff --git a/lib/towerops_web/live/device_live/show.ex b/lib/towerops_web/live/device_live/show.ex
index 2fbbb11d..e4ede254 100644
--- a/lib/towerops_web/live/device_live/show.ex
+++ b/lib/towerops_web/live/device_live/show.ex
@@ -367,19 +367,22 @@ defmodule ToweropsWeb.DeviceLive.Show do
       type: :cloud,
       name: "Cloud Polling",
       source: nil,
-      last_seen_at: nil
+      last_seen_at: nil,
+      is_offline: false
     }
   end
 
   defp load_agent_info(agent_token_id, source) do
     agent_token = Agents.get_agent_token!(agent_token_id)
+    is_offline = agent_offline?(agent_token)
 
     %{
       agent_token_id: agent_token_id,
       type: if(agent_token.is_cloud_poller, do: :cloud, else: :agent),
       name: agent_token.name,
       source: source,
-      last_seen_at: agent_token.last_seen_at
+      last_seen_at: agent_token.last_seen_at,
+      is_offline: is_offline
     }
   rescue
     Ecto.NoResultsError ->
@@ -389,10 +392,20 @@ defmodule ToweropsWeb.DeviceLive.Show do
         type: :cloud,
         name: "Cloud Polling (agent not found)",
         source: nil,
-        last_seen_at: nil
+        last_seen_at: nil,
+        is_offline: false
       }
   end
 
+  # Agent is considered offline if it hasn't been seen in the last 5 minutes
+  defp agent_offline?(%{is_cloud_poller: true}), do: false
+  defp agent_offline?(%{last_seen_at: nil}), do: true
+
+  defp agent_offline?(%{last_seen_at: last_seen_at}) do
+    five_minutes_ago = DateTime.add(DateTime.utc_now(), -5, :minute)
+    DateTime.before?(last_seen_at, five_minutes_ago)
+  end
+
   defp calculate_metrics(checks, _equipment) do
     total_checks = length(checks)
 
diff --git a/lib/towerops_web/live/device_live/show.html.heex b/lib/towerops_web/live/device_live/show.html.heex
index 90c5990d..313e5617 100644
--- a/lib/towerops_web/live/device_live/show.html.heex
+++ b/lib/towerops_web/live/device_live/show.html.heex
@@ -44,6 +44,14 @@
               <.icon name="hero-server" class="h-3.5 w-3.5" />
               {@agent_info.name}
             </span>
+            <%= if @agent_info.is_offline do %>
+              <span
+                class="inline-flex items-center gap-1 px-2 py-0.5 text-xs font-medium text-amber-700 bg-amber-100 dark:text-amber-400 dark:bg-amber-900/30 rounded-md"
+                title="Agent has not checked in for over 5 minutes. This device will not be polled until the agent comes back online."
+              >
+                <.icon name="hero-exclamation-triangle" class="h-3 w-3" /> Offline
+              </span>
+            <% end %>
             <%= if @agent_info.last_seen_at do %>
               <span class="text-xs text-gray-400 dark:text-gray-500">
                 ({format_relative_time(@agent_info.last_seen_at)})
diff --git a/test/towerops/agents_test.exs b/test/towerops/agents_test.exs
index 5844750e..6edf136c 100644
--- a/test/towerops/agents_test.exs
+++ b/test/towerops/agents_test.exs
@@ -1574,4 +1574,159 @@ defmodule Towerops.AgentsTest do
       # No assertion needed - just verify it doesn't crash
     end
   end
+
+  describe "should_phoenix_poll_device?/1" do
+    setup %{organization: org} do
+      {:ok, site} =
+        Towerops.Sites.create_site(%{
+          name: "Test Site",
+          organization_id: org.id
+        })
+
+      {:ok, device} =
+        Towerops.Devices.create_device(%{
+          name: "Test Device",
+          ip_address: "192.168.1.1",
+          site_id: site.id,
+          organization_id: org.id
+        })
+
+      {:ok, local_agent, _} = Agents.create_agent_token(org.id, "Local Agent")
+      {:ok, cloud_poller, _} = Agents.create_cloud_poller("Cloud Poller")
+
+      %{
+        site: site,
+        device: device,
+        local_agent: local_agent,
+        cloud_poller: cloud_poller
+      }
+    end
+
+    test "returns true when device has no agent assigned", %{device: device} do
+      device = Repo.preload(device, site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == true
+    end
+
+    test "returns true when device is assigned to cloud poller via direct assignment", %{
+      device: device,
+      cloud_poller: cloud_poller
+    } do
+      {:ok, _} = Agents.assign_device_to_agent(cloud_poller.id, device.id)
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == true
+    end
+
+    test "returns true when device inherits cloud poller from site", %{
+      device: device,
+      site: site,
+      cloud_poller: cloud_poller
+    } do
+      {:ok, _} = Towerops.Sites.update_site(site, %{agent_token_id: cloud_poller.id})
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == true
+    end
+
+    test "returns true when device inherits cloud poller from organization", %{
+      organization: org,
+      device: device,
+      cloud_poller: cloud_poller
+    } do
+      {:ok, _} = Towerops.Organizations.update_organization(org, %{default_agent_token_id: cloud_poller.id})
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == true
+    end
+
+    test "returns true when device inherits global cloud poller", %{device: device, cloud_poller: cloud_poller} do
+      {:ok, _} = Towerops.Settings.set_global_default_cloud_poller(cloud_poller.id)
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == true
+
+      # Clean up
+      {:ok, _} = Towerops.Settings.set_global_default_cloud_poller(nil)
+    end
+
+    test "returns false when device is assigned to local agent via direct assignment", %{
+      device: device,
+      local_agent: local_agent
+    } do
+      {:ok, _} = Agents.assign_device_to_agent(local_agent.id, device.id)
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == false
+    end
+
+    test "returns false when device inherits local agent from site", %{
+      device: device,
+      site: site,
+      local_agent: local_agent
+    } do
+      {:ok, _} = Towerops.Sites.update_site(site, %{agent_token_id: local_agent.id})
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == false
+    end
+
+    test "returns false when device inherits local agent from organization", %{
+      organization: org,
+      device: device,
+      local_agent: local_agent
+    } do
+      {:ok, _} = Towerops.Organizations.update_organization(org, %{default_agent_token_id: local_agent.id})
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      assert Agents.should_phoenix_poll_device?(device) == false
+    end
+
+    test "device-level assignment takes precedence over site/org (local overrides cloud)", %{
+      organization: org,
+      site: site,
+      device: device,
+      local_agent: local_agent,
+      cloud_poller: cloud_poller
+    } do
+      # Set cloud poller at org and site level
+      {:ok, _} = Towerops.Organizations.update_organization(org, %{default_agent_token_id: cloud_poller.id})
+      {:ok, _} = Towerops.Sites.update_site(site, %{agent_token_id: cloud_poller.id})
+
+      # But assign local agent at device level
+      {:ok, _} = Agents.assign_device_to_agent(local_agent.id, device.id)
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      # Should return false because device is assigned to local agent
+      assert Agents.should_phoenix_poll_device?(device) == false
+    end
+
+    test "device-level assignment takes precedence over site/org (cloud overrides local)", %{
+      organization: org,
+      site: site,
+      device: device,
+      local_agent: local_agent,
+      cloud_poller: cloud_poller
+    } do
+      # Set local agent at org and site level
+      {:ok, _} = Towerops.Organizations.update_organization(org, %{default_agent_token_id: local_agent.id})
+      {:ok, _} = Towerops.Sites.update_site(site, %{agent_token_id: local_agent.id})
+
+      # But assign cloud poller at device level
+      {:ok, _} = Agents.assign_device_to_agent(cloud_poller.id, device.id)
+
+      device = device |> Repo.reload!() |> Repo.preload(site: [organization: :default_agent_token])
+
+      # Should return true because device is assigned to cloud poller
+      assert Agents.should_phoenix_poll_device?(device) == true
+    end
+  end
 end