diff --git a/frappy_demo/test.py b/frappy_demo/test.py
index d851dfb..a86c777 100644
--- a/frappy_demo/test.py
+++ b/frappy_demo/test.py
@@ -26,7 +26,7 @@ from frappy.datatypes import FloatRange, StringType, ValueType, TupleOf, StructO
 from frappy.modules import Communicator, Drivable, Parameter, Property, Readable, Module, Attached
 from frappy.params import Command
 from frappy.dynamic import Pinata
-from frappy.errors import RangeError
+from frappy.errors import RangeError, HardwareError
 
 class Pin(Pinata):
     def scanModules(self):
@@ -72,8 +72,12 @@ class Heater(Drivable):
     maxheaterpower = Parameter('maximum allowed heater power',
                                datatype=FloatRange(0, 100), unit='W',
                                )
+    error_message = Parameter('simulated error message', StringType(),
+                              default='', readonly=False)
 
     def read_value(self):
+        if self.error_message:
+            raise HardwareError(self.error_message)
         return round(100 * random.random(), 1)
 
     def write_target(self, target):