diff --git a/src/km3io/tools.py b/src/km3io/tools.py
index ae6b015fe0c7da409c8f84d776dab02b241af522..30e32c7c2e0bdc5591229ecf344ce04a4ac241ae 100644
--- a/src/km3io/tools.py
+++ b/src/km3io/tools.py
@@ -556,3 +556,13 @@ def get_w2list_idx(f):
     sim_program = f.header.simul.program.lower()
     return w2s_idx.get(sim_program)
 
+
+def is_nanobeacon(trigger_mask):
+    """Returns True if the trigger mask contains the nano-beacon flag.
+
+    Parameters
+    ----------
+    trigger_mask : int or array(int)
+      A value or an array of the trigger_mask, either of an event, or a hit.
+    """
+    return is_bit_set(trigger_mask, ktrg.JTRIGGERNB)
diff --git a/tests/test_tools.py b/tests/test_tools.py
index 5cad5ffa48eacf2f08179b38fcd7d56e3e4916f6..c55cf6fecf52fc0b039a5faecb4124cdcec9ec61 100644
--- a/tests/test_tools.py
+++ b/tests/test_tools.py
@@ -31,6 +31,7 @@ from km3io.tools import (
     is_3dshower,
     is_mxshower,
     is_3dmuon,
+    is_nanobeacon,
 )
 
 OFFLINE_FILE = OfflineReader(data_path("offline/km3net_offline.root"))
@@ -642,3 +643,13 @@ class TestTriggerMaskChecks(unittest.TestCase):
             [False, False, False, True, False, False, True, False, True, True],
             list(is_3dmuon(GENHEN_OFFLINE_FILE.events.trigger_mask)),
         )
+
+    def test_is_nanobeacon(self):
+        assert np.allclose(
+            [False, False, False, False, False, False, False, False, False, False],
+            list(is_nanobeacon(OFFLINE_FILE.events.trigger_mask)),
+        )
+        assert np.allclose(
+            [False, False, False, False, False, False, False, False, False, False],
+            list(is_nanobeacon(GENHEN_OFFLINE_FILE.events.trigger_mask)),
+        )