diff --git a/priv/repo/migrations/20260125183652_add_missing_sensor_units.exs b/priv/repo/migrations/20260125183652_add_missing_sensor_units.exs
new file mode 100644
index 00000000..1533a905
--- /dev/null
+++ b/priv/repo/migrations/20260125183652_add_missing_sensor_units.exs
@@ -0,0 +1,62 @@
+defmodule Towerops.Repo.Migrations.AddMissingSensorUnits do
+  use Ecto.Migration
+
+  def up do
+    # Set sensor_unit for all sensors that are missing it
+    # This fixes sensors created before sensor_unit was properly set in discovery code
+
+    # Temperature sensors
+    execute """
+    UPDATE snmp_sensors
+    SET sensor_unit = '°C'
+    WHERE sensor_type = 'temperature'
+      AND (sensor_unit IS NULL OR sensor_unit = '')
+    """
+
+    # Voltage sensors (only those without unit set)
+    execute """
+    UPDATE snmp_sensors
+    SET sensor_unit = 'V'
+    WHERE sensor_type = 'voltage'
+      AND (sensor_unit IS NULL OR sensor_unit = '')
+    """
+
+    # Current sensors
+    execute """
+    UPDATE snmp_sensors
+    SET sensor_unit = 'mA'
+    WHERE sensor_type = 'current'
+      AND (sensor_unit IS NULL OR sensor_unit = '')
+    """
+
+    # Power sensors
+    execute """
+    UPDATE snmp_sensors
+    SET sensor_unit = 'W'
+    WHERE sensor_type = 'power'
+      AND (sensor_unit IS NULL OR sensor_unit = '')
+    """
+
+    # dBm sensors (optical power)
+    execute """
+    UPDATE snmp_sensors
+    SET sensor_unit = 'dBm'
+    WHERE sensor_type = 'dbm'
+      AND (sensor_unit IS NULL OR sensor_unit = '')
+    """
+
+    # State sensors (leave empty, they don't have units)
+    # Fan speed sensors should already have RPM
+    # Frequency, rate, etc. should already have their units
+  end
+
+  def down do
+    # Revert by setting units back to empty string
+    execute """
+    UPDATE snmp_sensors
+    SET sensor_unit = ''
+    WHERE sensor_type IN ('temperature', 'voltage', 'current', 'power', 'dbm')
+      AND sensor_unit IN ('°C', 'V', 'mA', 'W', 'dBm')
+    """
+  end
+end