diff --git a/alarmdecoder/decoder.py b/alarmdecoder/decoder.py
index 9398c1f..73d3a92 100644
--- a/alarmdecoder/decoder.py
+++ b/alarmdecoder/decoder.py
@@ -25,7 +25,7 @@ class AlarmDecoder(object):
     on_arm = event.Event("This event is called when the panel is armed.\n\n**Callback definition:** *def callback(device)*")
     on_disarm = event.Event("This event is called when the panel is disarmed.\n\n**Callback definition:** *def callback(device)*")
     on_power_changed = event.Event("This event is called when panel power switches between AC and DC.\n\n**Callback definition:** *def callback(device, status)*")
-    on_alarm = event.Event("This event is called when the alarm is triggered.\n\n**Callback definition:** *def callback(device, status)*")
+    on_alarm = event.Event("This event is called when the alarm is triggered.\n\n**Callback definition:** *def callback(device, status, zone)*")
     on_fire = event.Event("This event is called when a fire is detected.\n\n**Callback definition:** *def callback(device, status)*")
     on_bypass = event.Event("This event is called when a zone is bypassed.  \n\n\n\n**Callback definition:** *def callback(device, status)*")
     on_boot = event.Event("This event is called when the device finishes booting.\n\n**Callback definition:** *def callback(device)*")