diff --git a/aodh/api/controllers/v2/alarms.py b/aodh/api/controllers/v2/alarms.py
index e4360738e..4d6938004 100644
--- a/aodh/api/controllers/v2/alarms.py
+++ b/aodh/api/controllers/v2/alarms.py
@@ -21,8 +21,10 @@
 import datetime
 import itertools
 import json
+import warnings
 
 import croniter
+import debtcollector
 from oslo_config import cfg
 from oslo_log import log
 from oslo_utils import netutils
@@ -265,6 +267,12 @@ class Alarm(base.Base):
 
     @staticmethod
     def validate(alarm):
+        if alarm.type == 'threshold':
+            warnings.simplefilter("always")
+            debtcollector.deprecate(
+                "Ceilometer's API is deprecated as of Ocata. Therefore, "
+                " threshold rule alarms are no longer supported.",
+                version="5.0.0")
 
         Alarm.check_rule(alarm)
         Alarm.check_alarm_actions(alarm)
diff --git a/releasenotes/notes/deprecate-threshold-alarm-d89da351d4f6f50f.yaml b/releasenotes/notes/deprecate-threshold-alarm-d89da351d4f6f50f.yaml
new file mode 100644
index 000000000..3d4f54658
--- /dev/null
+++ b/releasenotes/notes/deprecate-threshold-alarm-d89da351d4f6f50f.yaml
@@ -0,0 +1,9 @@
+---
+deprecations:
+  - |
+    Ceilometer's API is deprecated in Ocata. Therefore, threshold alarms are
+    now deprecated as well. Threshold rules will be removed when Ceilometer's
+    API is also removed. Similar functionality is provided through Gnocchi
+    alarm rules: ``gnocchi_resources_threshold``,
+    ``gnocchi_aggregation_by_metrics_threshold``, or
+    ``gnocchi_aggregation_by_resources_threshold``.
diff --git a/requirements.txt b/requirements.txt
index 92d2e4587..b73df314c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -34,3 +34,4 @@ WSME>=0.8
 cachetools>=1.1.6
 cotyledon
 keystoneauth1>=2.1
+debtcollector>=1.2.0  # Apache-2.0