diff --git a/brmbar3/brmbar-gui-qt4.py b/brmbar3/brmbar-gui-qt4.py
index 429aeb6..a351bee 100755
--- a/brmbar3/brmbar-gui-qt4.py
+++ b/brmbar3/brmbar-gui-qt4.py
@@ -1,6 +1,7 @@
 #!/usr/bin/python3
 
 import sys
+import subprocess
 
 from PySide import QtCore, QtGui, QtDeclarative
 
@@ -10,6 +11,12 @@ import brmbar
 
 # User credit balance limit; sale will fail when balance is below this limit.
 LIMIT_BALANCE = -200
+# When below this credit balance, an alert hook script (see below) is run.
+ALERT_BALANCE = 0
+# This script is executed when a user is buying things and their balance is
+# below LIMIT_BALANCE (with argument "limit") or below ALERT_BALANCE
+# (with argument "alert").
+ALERT_SCRIPT = "./alert.sh"
 
 
 class ShopAdapter(QtCore.QObject):
@@ -76,7 +83,14 @@ class ShopAdapter(QtCore.QObject):
     @QtCore.Slot('QVariant', 'QVariant', result='QVariant')
     def canSellItem(self, itemid, userid):
         user = brmbar.Account.load(db, id = userid)
-        return -user.balance() > LIMIT_BALANCE
+        if -user.balance() > ALERT_BALANCE:
+            return True
+        elif -user.balance() > LIMIT_BALANCE:
+            subprocess.call(["sh", ALERT_SCRIPT, "alert"])
+            return True
+        else:
+            subprocess.call(["sh", ALERT_SCRIPT, "limit"])
+            return False
 
     @QtCore.Slot('QVariant', 'QVariant', result='QVariant')
     def sellItem(self, itemid, userid):