diff --git a/check_modem.py b/check_modem.py
index cae4da8..19f9ed1 100755
--- a/check_modem.py
+++ b/check_modem.py
@@ -4,6 +4,7 @@ import logging
 import os
 import sys
 import time
+from enum import IntEnum
 from pydbus import SystemBus
 from gi.repository import GLib
 import sms_functions
@@ -28,19 +29,20 @@ import sms_functions
 #  * Enumeration of possible modem states.
 #  */
 # mm_modem_state
-MM_MODEM_STATE_FAILED        = -1
-MM_MODEM_STATE_UNKNOWN       = 0
-MM_MODEM_STATE_INITIALIZING  = 1
-MM_MODEM_STATE_LOCKED        = 2
-MM_MODEM_STATE_DISABLED      = 3
-MM_MODEM_STATE_DISABLING     = 4
-MM_MODEM_STATE_ENABLING      = 5
-MM_MODEM_STATE_ENABLED       = 6
-MM_MODEM_STATE_SEARCHING     = 7
-MM_MODEM_STATE_REGISTERED    = 8
-MM_MODEM_STATE_DISCONNECTING = 9
-MM_MODEM_STATE_CONNECTING    = 10
-MM_MODEM_STATE_CONNECTED     = 11
+class MMModemState(IntEnum):
+    FAILED        = -1
+    UNKNOWN       = 0
+    INITIALIZING  = 1
+    LOCKED        = 2
+    DISABLED      = 3
+    DISABLING     = 4
+    ENABLING      = 5
+    ENABLED       = 6
+    SEARCHING     = 7
+    REGISTERED    = 8
+    DISCONNECTING = 9
+    CONNECTING    = 10
+    CONNECTED     = 11
 
 # Setup logging
 logfile = "/opt/sms/sms.log"
@@ -49,14 +51,28 @@ logging.basicConfig(format=FORMAT,filename=logfile,level=10)
 logger = logging.getLogger('check_modem')
 
 if __name__ == "__main__":
+    exit_code = 3   # Unknown (for Nagios)
+
     modem = sms_functions.unlock_and_enable_modem()
     time.sleep(2)
     modem = sms_functions.get_modem()
-    status = modem.GetStatus()
-    print(status)
     
+    status = modem.GetStatus()
+    status['state_text'] = MMModemState(status['state']).name
+
     # return code: if registered and signal > 0, return 0
-    if modem.GetStatus()["state"] in [ MM_MODEM_STATE_REGISTERED, MM_MODEM_STATE_CONNECTED ] and modem.SignalQuality[0] > 0 and modem.RegistrationState == 1:
-        exit(0)
+    if modem.GetStatus()["state"] in [ MMModemState.REGISTERED, MMModemState.CONNECTED ] and modem.SignalQuality[0] > 0 and modem.RegistrationState == 1:
+        print("OK: ", end='')
+        exit_code = 0
+    elif modem.GetStatus()["state"] in [ MMModemState.INITIALIZING, MMModemState.ENABLED, MMModemState.SEARCHING, MMModemState.DISCONNECTING ]:
+        print("WARNING: ", end='')
+        exit_code = 1
+    elif modem.GetStatus()["state"] in [ MMModemState.FAILED, MMModemState.LOCKED, MMModemState.DISABLED ]:
+        print("CRITICAL: ", end='')
+        exit_code = 2
     else:
-        exit(1)
+        print("UNKNOWN: ", end='')
+        exit_code = 3
+    
+    print(status)
+    exit(exit_code)