diff --git a/csaxs_bec/device_configs/bl_detectors.yaml b/csaxs_bec/device_configs/bl_detectors.yaml
index 74cbc7b4..be88dd87 100644
--- a/csaxs_bec/device_configs/bl_detectors.yaml
+++ b/csaxs_bec/device_configs/bl_detectors.yaml
@@ -1,23 +1,16 @@
-eiger2_si_500k:
-  description: Eiger 2 Si 500K detector
-  deviceClass: csaxs_bec.devices.jungfraujoch.eiger2_si_500k.Eiger2Si500K
-  deviceConfig:
-    detector_distance: 1000
-    beam_center: [200, 200]
-  onFailure: raise
-  enabled: True
-  readoutPriority: async
-  softwareTrigger: False
-  deviceTags:
-    - bl_detectors
-    - eiger
+# Eiger detectors (JungfrauJoch). Only one may be enabled at a time -- the JFJ broker
+# serves a single selected/initialised detector, so switching the active one here also
+# requires selecting/initialising the matching detector on the JFJ broker itself.
+# JungfrauJoch-side config (detector selection/init, pixel mask, azimuthal integration
+# settings) is done in the Web UI at http://sls-jfjoch-001.psi.ch:8080.
+# The Eiger 2 Si 500K detector server itself is reachable at 129.129.122.159.
+# eiger2_si_500k:
 
-# eiger_1_5:
-#   description: Eiger 1.5M in-vacuum detector
-#   deviceClass: csaxs_bec.devices.jungfraujoch.eiger_1_5m.Eiger1_5M
+#   description: Eiger 2 Si 500K detector
+#   deviceClass: csaxs_bec.devices.jungfraujoch.eiger2_si_500k.Eiger2Si500K
 #   deviceConfig:
-#     detector_distance: 2200
-#     beam_center: [870, 1203]
+#     detector_distance: 1000
+#     beam_center: [200, 200]
 #   onFailure: raise
 #   enabled: True
 #   readoutPriority: async
@@ -26,6 +19,20 @@ eiger2_si_500k:
 #     - bl_detectors
 #     - eiger
 
+eiger_1_5:
+  description: Eiger 1.5M in-vacuum detector
+  deviceClass: csaxs_bec.devices.jungfraujoch.eiger_1_5m.Eiger1_5M
+  deviceConfig:
+    detector_distance: 2200
+    beam_center: [870, 1203]
+  onFailure: raise
+  enabled: True
+  readoutPriority: async
+  softwareTrigger: False
+  deviceTags:
+    - bl_detectors
+    - eiger
+
 # eiger_9:
 #   description: Eiger 9M detector
 #   deviceClass: csaxs_bec.devices.jungfraujoch.eiger_9m.Eiger9M
diff --git a/csaxs_bec/devices/jungfraujoch/eiger.py b/csaxs_bec/devices/jungfraujoch/eiger.py
index 6e41a007..c597ac10 100644
--- a/csaxs_bec/devices/jungfraujoch/eiger.py
+++ b/csaxs_bec/devices/jungfraujoch/eiger.py
@@ -226,11 +226,18 @@ class Eiger(PSIDeviceBase):
             message (dict): The message received from the preview stream.
         """
         if message.get("type", "") == "image":
-            data = message.get("data", {}).get("default", None)
-            if data is None:
+            channels = message.get("data", {})
+            # The data dict's key varies by detector: "default" for eiger_1_5/eiger_9,
+            # but a threshold name (e.g. "threshold_1") for the multi-threshold-capable
+            # Eiger2 Si 500K. Prefer "default" when present, else take whichever single
+            # channel the broker actually sent.
+            frame = channels.get("default")
+            if frame is None:
+                frame = next(iter(channels.values()), None)
+            if frame is None:
                 logger.error(f"Received image message on device {self.name} without data.")
                 return
-            self.preview_image.put(data)
+            self.preview_image.put(frame)
 
     # pylint: disable=missing-function-docstring
     @property
diff --git a/tests/tests_devices/test_eiger.py b/tests/tests_devices/test_eiger.py
index 5e036de5..979494c2 100644
--- a/tests/tests_devices/test_eiger.py
+++ b/tests/tests_devices/test_eiger.py
@@ -542,6 +542,29 @@ def test_eiger_preview_callback(eiger_1_5m):
                 mock_preview_put.assert_not_called()
 
 
+def test_eiger_preview_callback_falls_back_to_non_default_channel(eiger2_si_500k):
+    """The Eiger2 Si 500K's multi-threshold preview data has no "default" key (it's
+    named after the threshold, e.g. "threshold_1" -- confirmed against a live capture
+    of the JFJ preview stream); the callback must still forward that single channel.
+    """
+    eiger = eiger2_si_500k
+    frame = np.array([[1, 2], [3, 4]])
+    msg = {"type": "image", "data": {"threshold_1": frame}}
+    with mock.patch.object(eiger.preview_image, "put") as mock_preview_put:
+        eiger._preview_callback(msg)
+        mock_preview_put.assert_called_once_with(frame)
+
+
+def test_eiger_preview_callback_logs_when_data_is_truly_empty(eiger_1_5m):
+    """No channel at all (empty or missing data dict) must still be treated as missing,
+    not silently pass through some other unrelated dict key."""
+    eiger = eiger_1_5m
+    for msg in [{"type": "image", "data": {}}, {"type": "image"}]:
+        with mock.patch.object(eiger.preview_image, "put") as mock_preview_put:
+            eiger._preview_callback(msg)
+            mock_preview_put.assert_not_called()
+
+
 def test_eiger_acquisition_matches_the_gated_window(eiger_1_5m):
     """The detector must acquire for exp_time - readout, not for the whole period.