diff --git a/pyaci/aci/AciEvent.py b/pyaci/aci/AciEvent.py
index 28d99b4..dc34d3e 100644
--- a/pyaci/aci/AciEvent.py
+++ b/pyaci/aci/AciEvent.py
@@ -163,7 +163,7 @@ def __init__(self,pkt):
 class HeartbeatMsg(object):
     def __init__(self, data):
         if len(data) != 18:
-            print(str.format("Error: expected 18 bytes, got %s" %(data)))
+            raise ValueError("Error: expected 18 bytes, got %s" % data)
         (self.rssi, self.received_at, self.received_at_ms, self.local_clock_version, self.sensor_id, self.epoch_seconds, self.epoch_ms, self.clock_version) = unpack('<BiHHBiHH', bytearray(data))
 
     def __repr__(self):
diff --git a/pyaci/aci_serial/AciUart.py b/pyaci/aci_serial/AciUart.py
index 46212b5..b96bb8b 100644
--- a/pyaci/aci_serial/AciUart.py
+++ b/pyaci/aci_serial/AciUart.py
@@ -57,14 +57,15 @@ def ProcessCommand(self, command):
                 logging.error('traceback: %s', traceback.format_exc())
 
     def write_aci_cmd(self, cmd):
+        retval = None
         if isinstance(cmd,AciCommand.AciCommandPkt):
             self.WriteData(cmd.serialize())
             retval = self.Wait(self)
-            print("Events received: %s" %retval)
             if retval == None:
                 logging.info('cmd %s, timeout waiting for event' % (cmd.__class__.__name__))
         else:
             logging.error('The command provided is not valid: %s\nIt must be an instance of the AciCommandPkt class (or one of its subclasses)', str(cmd))
+        return retval
 
 
 
diff --git a/pyaci/upload.py b/pyaci/upload.py
index 5f5e719..2bbdd75 100755
--- a/pyaci/upload.py
+++ b/pyaci/upload.py
@@ -53,7 +53,9 @@ def get_sensor_updates(self):
 
     def run_app_command(self, command):
         data = command.serialize()
-        return self.aci.write_aci_cmd(AciCommand.AciAppCommand(data=data,length=len(data)+1))
+        retval = self.aci.write_aci_cmd(AciCommand.AciAppCommand(data=data,length=len(data)+1))
+        print("Events received: %s" % retval)
+        return retval
 
     def sync_time(self):
         self.last_time_sync = time.time()