diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Alarms/AlarmConditionState.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Alarms/AlarmConditionState.cs
new file mode 100644
index 00000000..b8b57a63
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Alarms/AlarmConditionState.cs
@@ -0,0 +1,24 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Alarms;
+
+/// <summary>
+/// Unified, read-only alarm condition state. The OPC UA Part 9 sub-conditions
+/// are orthogonal, and MxAccess's ACTIVE / ACTIVE_ACKED / INACTIVE map cleanly
+/// onto them, so they are modeled as independent flags plus a 0–1000 severity.
+/// Computed alarms populate this from State + Priority; native alarms mirror it
+/// from the source.
+/// </summary>
+/// <param name="Active">Active vs Inactive.</param>
+/// <param name="Acknowledged">Acked vs Unacked.</param>
+/// <param name="Confirmed">Confirmed vs Unconfirmed; null when the condition is not confirmable.</param>
+/// <param name="Shelve">Shelving sub-state.</param>
+/// <param name="Suppressed">Whether the source has suppressed the condition.</param>
+/// <param name="Severity">Severity on the unified 0–1000 scale.</param>
+public record AlarmConditionState(
+    bool Active,
+    bool Acknowledged,
+    bool? Confirmed,
+    AlarmShelveState Shelve,
+    bool Suppressed,
+    int Severity);
diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Alarms/NativeAlarmTransition.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Alarms/NativeAlarmTransition.cs
new file mode 100644
index 00000000..02cbeb6e
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Alarms/NativeAlarmTransition.cs
@@ -0,0 +1,39 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Alarms;
+
+/// <summary>
+/// Protocol-neutral alarm transition emitted by an
+/// <c>IAlarmSubscribableConnection</c> adapter (OPC UA A&amp;C or MxGateway).
+/// Keyed by <see cref="SourceReference"/>; routed to instances by
+/// <see cref="SourceObjectReference"/>.
+/// </summary>
+/// <param name="SourceReference">Stable per-condition key (e.g. "Tank01.Level.HiHi").</param>
+/// <param name="SourceObjectReference">Owning source object used for instance routing (e.g. "Tank01").</param>
+/// <param name="AlarmTypeName">Source alarm type (e.g. "AnalogLimitAlarm.HiHi").</param>
+/// <param name="Kind">Transition classification, incl. snapshot replay sentinels.</param>
+/// <param name="Condition">Mirrored condition state.</param>
+/// <param name="Category">Source taxonomy/category.</param>
+/// <param name="Description">Human-readable description from the source template.</param>
+/// <param name="Message">Event message text.</param>
+/// <param name="OperatorUser">Operator principal on ack transitions (display-only).</param>
+/// <param name="OperatorComment">Operator comment on ack transitions (display-only).</param>
+/// <param name="OriginalRaiseTime">When the condition originally became active, if known.</param>
+/// <param name="TransitionTime">When this transition occurred.</param>
+/// <param name="CurrentValue">Current source value (display-only).</param>
+/// <param name="LimitValue">Limit/threshold value for limit alarms (display-only).</param>
+public record NativeAlarmTransition(
+    string SourceReference,
+    string SourceObjectReference,
+    string AlarmTypeName,
+    AlarmTransitionKind Kind,
+    AlarmConditionState Condition,
+    string Category,
+    string Description,
+    string Message,
+    string OperatorUser,
+    string OperatorComment,
+    DateTimeOffset? OriginalRaiseTime,
+    DateTimeOffset TransitionTime,
+    string CurrentValue,
+    string LimitValue);
diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmKind.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmKind.cs
new file mode 100644
index 00000000..cb99bbc7
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmKind.cs
@@ -0,0 +1,17 @@
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+/// <summary>
+/// Distinguishes how an alarm's state is produced: computed at the site from
+/// attribute triggers, or mirrored read-only from a native source.
+/// </summary>
+public enum AlarmKind
+{
+    /// <summary>Evaluated at the site by an AlarmActor from attribute triggers.</summary>
+    Computed,
+
+    /// <summary>Mirrored from an OPC UA Alarms &amp; Conditions server.</summary>
+    NativeOpcUa,
+
+    /// <summary>Mirrored from the MxAccess Gateway alarm feed.</summary>
+    NativeMxAccess
+}
diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmShelveState.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmShelveState.cs
new file mode 100644
index 00000000..d6f28274
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmShelveState.cs
@@ -0,0 +1,13 @@
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+/// <summary>
+/// OPC UA Part 9 shelving sub-state of an alarm condition. Mirrored read-only
+/// from the source; computed alarms are always <see cref="Unshelved"/>.
+/// </summary>
+public enum AlarmShelveState
+{
+    Unshelved,
+    OneShotShelved,
+    TimedShelved,
+    PermanentShelved
+}
diff --git a/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmTransitionKind.cs b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmTransitionKind.cs
new file mode 100644
index 00000000..96cb23e6
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.Commons/Types/Enums/AlarmTransitionKind.cs
@@ -0,0 +1,18 @@
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+/// <summary>
+/// Classifies a <c>NativeAlarmTransition</c> emitted by an
+/// <c>IAlarmSubscribableConnection</c> adapter. <see cref="Snapshot"/> and
+/// <see cref="SnapshotComplete"/> carry the initial active-condition replay
+/// produced on every (re)subscribe so consumers can re-seed state.
+/// </summary>
+public enum AlarmTransitionKind
+{
+    Snapshot,
+    SnapshotComplete,
+    Raise,
+    Acknowledge,
+    Clear,
+    Retrigger,
+    StateChange
+}
diff --git a/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/Alarms/AlarmConditionStateTests.cs b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/Alarms/AlarmConditionStateTests.cs
new file mode 100644
index 00000000..376a52e5
--- /dev/null
+++ b/tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/Alarms/AlarmConditionStateTests.cs
@@ -0,0 +1,36 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Alarms;
+using ZB.MOM.WW.ScadaBridge.Commons.Types.Enums;
+
+namespace ZB.MOM.WW.ScadaBridge.Commons.Tests.Types.Alarms;
+
+public class AlarmConditionStateTests
+{
+    [Fact]
+    public void AlarmConditionState_DefaultsAreNormalUnshelved()
+    {
+        var s = new AlarmConditionState(
+            Active: false, Acknowledged: true, Confirmed: null,
+            Shelve: AlarmShelveState.Unshelved, Suppressed: false, Severity: 0);
+
+        Assert.False(s.Active);
+        Assert.Equal(AlarmShelveState.Unshelved, s.Shelve);
+        Assert.Equal(0, s.Severity);
+    }
+
+    [Fact]
+    public void NativeAlarmTransition_CarriesSourceAndCondition()
+    {
+        var t = new NativeAlarmTransition(
+            SourceReference: "Tank01.Level.HiHi", SourceObjectReference: "Tank01",
+            AlarmTypeName: "AnalogLimitAlarm.HiHi", Kind: AlarmTransitionKind.Raise,
+            Condition: new AlarmConditionState(true, false, null, AlarmShelveState.Unshelved, false, 800),
+            Category: "Process", Description: "High level", Message: "level high",
+            OperatorUser: "", OperatorComment: "",
+            OriginalRaiseTime: null, TransitionTime: DateTimeOffset.UnixEpoch,
+            CurrentValue: "92.1", LimitValue: "90");
+
+        Assert.Equal("Tank01", t.SourceObjectReference);
+        Assert.Equal(800, t.Condition.Severity);
+        Assert.Equal(AlarmTransitionKind.Raise, t.Kind);
+    }
+}