diff --git a/src/ScadaLink.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor b/src/ScadaLink.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor
index 3caf440..7f8531f 100644
--- a/src/ScadaLink.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor
+++ b/src/ScadaLink.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor
@@ -7,10 +7,12 @@
 @using ScadaLink.Commons.Types.Enums
 @using ScadaLink.TemplateEngine.Flattening
 @using ScadaLink.TemplateEngine.Services
+@using ScadaLink.DeploymentManager
 @attribute [Authorize(Policy = AuthorizationPolicies.RequireDeployment)]
 @inject ITemplateEngineRepository TemplateEngineRepository
 @inject ISiteRepository SiteRepository
 @inject InstanceService InstanceService
+@inject IFlatteningPipeline FlatteningPipeline
 @inject AuthenticationStateProvider AuthStateProvider
 @inject NavigationManager NavigationManager
 
@@ -353,6 +355,12 @@
     private string? _editingError;
     private IReadOnlyList<AlarmAttributeChoice> _editingAvailableAttributes = Array.Empty<AlarmAttributeChoice>();
 
+    // Cached flattened attribute list (direct + inherited + composed members,
+    // path-qualified canonical names). Populated once after the instance loads
+    // and fed to the alarm trigger editor so composed-member paths like
+    // "AlarmSensor.SensorReading" resolve in the picker.
+    private IReadOnlyList<AlarmAttributeChoice> _flattenedAttributes = Array.Empty<AlarmAttributeChoice>();
+
     // Area
     private List<Area> _siteAreas = new();
     private int _reassignAreaId;
@@ -405,6 +413,8 @@
             {
                 _existingAlarmOverrides[o.AlarmCanonicalName] = o;
             }
+
+            _flattenedAttributes = await BuildFlattenedAttributesAsync();
         }
         catch (Exception ex)
         {
@@ -547,9 +557,7 @@
             : (existing?.TriggerConfigurationOverride ?? alarm.TriggerConfiguration);
 
         _editingPriorityText = existing?.PriorityLevelOverride?.ToString();
-        _editingAvailableAttributes = _overrideAttrs
-            .Select(a => new AlarmAttributeChoice(a.Name, MapDataType(a.DataType), "Direct"))
-            .ToList();
+        _editingAvailableAttributes = _flattenedAttributes;
     }
 
     private void CancelEditOverride()
@@ -689,6 +697,47 @@
         _ => "Object"
     };
 
+    /// <summary>
+    /// Same mapping for the string form emitted by <see cref="Commons.Types.Flattening.ResolvedAttribute.DataType"/>.
+    /// </summary>
+    private static string MapDataType(string dt) =>
+        Enum.TryParse<DataType>(dt, out var parsed) ? MapDataType(parsed) : dt;
+
+    /// <summary>
+    /// Builds the alarm picker choice list from the flattened configuration so
+    /// composed-member paths (e.g. <c>AlarmSensor.SensorReading</c>) and
+    /// inherited attributes appear alongside direct ones. Falls back to the
+    /// direct-only list if flattening fails for any reason.
+    /// </summary>
+    private async Task<IReadOnlyList<AlarmAttributeChoice>> BuildFlattenedAttributesAsync()
+    {
+        var fallback = (IReadOnlyList<AlarmAttributeChoice>)_overrideAttrs
+            .Select(a => new AlarmAttributeChoice(a.Name, MapDataType(a.DataType), "Direct"))
+            .ToList();
+
+        try
+        {
+            var flat = await FlatteningPipeline.FlattenAndValidateAsync(Id);
+            if (flat.IsFailure) return fallback;
+
+            return flat.Value.Configuration.Attributes
+                .Select(a => new AlarmAttributeChoice(
+                    a.CanonicalName,
+                    MapDataType(a.DataType),
+                    a.Source switch
+                    {
+                        "Composed" => "Composed",
+                        "Inherited" => "Inherited",
+                        _ => "Direct" // Template / Override
+                    }))
+                .ToList();
+        }
+        catch
+        {
+            return fallback;
+        }
+    }
+
     // ── Area ────────────────────────────────────────────────
 
     private async Task ReassignArea()
diff --git a/src/ScadaLink.DeploymentManager/FlatteningPipeline.cs b/src/ScadaLink.DeploymentManager/FlatteningPipeline.cs
index cbd7a3a..1c6028b 100644
--- a/src/ScadaLink.DeploymentManager/FlatteningPipeline.cs
+++ b/src/ScadaLink.DeploymentManager/FlatteningPipeline.cs
@@ -50,23 +50,34 @@ public class FlatteningPipeline : IFlatteningPipeline
         if (templateChain.Count == 0)
             return Result<FlatteningPipelineResult>.Failure("Template chain is empty.");
 
-        // Build composition maps
+        // Build composition maps, walking nested compositions so the flattener
+        // can resolve composed-of-composed attributes / alarms / scripts (e.g.
+        // a parent that composes Pump where Pump itself composes AlarmSensor
+        // produces "Pump.AlarmSensor.SensorReading").
         var compositionMap = new Dictionary<int, IReadOnlyList<Commons.Entities.Templates.TemplateComposition>>();
         var composedChains = new Dictionary<int, IReadOnlyList<Commons.Entities.Templates.Template>>();
+        var processedTemplateIds = new HashSet<int>();
+        var pendingChains = new Queue<IReadOnlyList<Commons.Entities.Templates.Template>>();
 
-        foreach (var template in templateChain)
+        pendingChains.Enqueue(templateChain);
+        while (pendingChains.Count > 0)
         {
-            var compositions = await _templateRepo.GetCompositionsByTemplateIdAsync(template.Id, cancellationToken);
-            if (compositions.Count > 0)
+            var chain = pendingChains.Dequeue();
+            foreach (var template in chain)
             {
+                if (!processedTemplateIds.Add(template.Id)) continue;
+
+                var compositions = await _templateRepo.GetCompositionsByTemplateIdAsync(template.Id, cancellationToken);
+                if (compositions.Count == 0) continue;
+
                 compositionMap[template.Id] = compositions;
                 foreach (var comp in compositions)
                 {
-                    if (!composedChains.ContainsKey(comp.ComposedTemplateId))
-                    {
-                        composedChains[comp.ComposedTemplateId] =
-                            await BuildTemplateChainAsync(comp.ComposedTemplateId, cancellationToken);
-                    }
+                    if (composedChains.ContainsKey(comp.ComposedTemplateId)) continue;
+
+                    var composedChain = await BuildTemplateChainAsync(comp.ComposedTemplateId, cancellationToken);
+                    composedChains[comp.ComposedTemplateId] = composedChain;
+                    pendingChains.Enqueue(composedChain);
                 }
             }
         }
diff --git a/src/ScadaLink.TemplateEngine/Validation/ValidationService.cs b/src/ScadaLink.TemplateEngine/Validation/ValidationService.cs
index 04c7f22..cd2053c 100644
--- a/src/ScadaLink.TemplateEngine/Validation/ValidationService.cs
+++ b/src/ScadaLink.TemplateEngine/Validation/ValidationService.cs
@@ -220,11 +220,16 @@ public class ValidationService
 
     internal static string? ExtractAttributeNameFromTriggerConfig(string triggerConfigJson)
     {
+        // Accept both keys to stay consistent with FlatteningService.PrefixTriggerAttribute,
+        // AlarmActor.ParseEvalConfig and AlarmTriggerConfigCodec. Old data may still use
+        // "attribute"; the UI codec writes the canonical "attributeName".
         try
         {
             using var doc = JsonDocument.Parse(triggerConfigJson);
             if (doc.RootElement.TryGetProperty("attributeName", out var prop))
                 return prop.GetString();
+            if (doc.RootElement.TryGetProperty("attribute", out var legacyProp))
+                return legacyProp.GetString();
         }
         catch (JsonException)
         {