diff --git a/doc/revpimodio2.helper.html b/doc/revpimodio2.helper.html
index ee90dfb..5859e23 100644
--- a/doc/revpimodio2.helper.html
+++ b/doc/revpimodio2.helper.html
@@ -513,6 +513,11 @@ Aktiviert oder Deaktiviert die Eventueberwachung.
 <dd>
 True aktiviert / False deaktiviert
 </dd>
+</dl><dl>
+<dt>Returns:</dt>
+<dd>
+True, wenn Anforderung erfolgreich war
+</dd>
 </dl><a NAME="ProcimgWriter._get_ioerrors" ID="ProcimgWriter._get_ioerrors"></a>
 <h3 style="background-color:#FFFFFF;color:#FF0000">
 ProcimgWriter._get_ioerrors</h3>
diff --git a/revpimodio2/device.py b/revpimodio2/device.py
index 7754ecc..14e4d36 100644
--- a/revpimodio2/device.py
+++ b/revpimodio2/device.py
@@ -284,9 +284,8 @@ class Device(object):
             self._modio.readprocimg(self)
 
             # Datenkopie anlegen
-            self._filelock.acquire()
-            self._ba_datacp = self._ba_devdata[:]
-            self._filelock.release()
+            with self._filelock:
+                self._ba_datacp = self._ba_devdata[:]
 
             self._selfupdate = True
 
diff --git a/revpimodio2/helper.py b/revpimodio2/helper.py
index b79c2df..24b67de 100644
--- a/revpimodio2/helper.py
+++ b/revpimodio2/helper.py
@@ -384,10 +384,16 @@ class ProcimgWriter(Thread):
 
     def _collect_events(self, value):
         """Aktiviert oder Deaktiviert die Eventueberwachung.
-        @param value True aktiviert / False deaktiviert"""
+        @param value True aktiviert / False deaktiviert
+        @return True, wenn Anforderung erfolgreich war"""
         if type(value) != bool:
             raise ValueError("value must be <class 'bool'>")
 
+        # Nur starten, wenn System läuft
+        if not self.is_alive():
+            self.__eventwork = False
+            return False
+
         if self.__eventwork != value:
             with self.lck_refresh:
                 self.__eventwork = value
@@ -401,6 +407,8 @@ class ProcimgWriter(Thread):
                 self.__eventth.daemon = True
                 self.__eventth.start()
 
+        return True
+
     def _get_ioerrors(self):
         """Ruft aktuelle Anzahl der Fehler ab.
         @return Aktuelle Fehleranzahl"""
@@ -456,13 +464,13 @@ class ProcimgWriter(Thread):
                 if self._modio._monitoring:
                     # Inputs und Outputs in Puffer
                     for dev in self._modio._lst_refresh:
-                        dev._filelock.acquire()
-                        dev._ba_devdata[:] = bytesbuff[dev._slc_devoff]
-                        if self.__eventwork \
-                                and len(dev._dict_events) > 0 \
-                                and dev._ba_datacp != dev._ba_devdata:
-                            self.__check_change(dev)
-                        dev._filelock.release()
+                        with dev._filelock:
+                            dev._ba_devdata[:] = bytesbuff[dev._slc_devoff]
+                            if self.__eventwork \
+                                    and len(dev._dict_events) > 0 \
+                                    and dev._ba_datacp != dev._ba_devdata:
+                                self.__check_change(dev)
+
                 else:
                     # Inputs in Puffer, Outputs in Prozessabbild
                     for dev in self._modio._lst_refresh:
@@ -493,7 +501,7 @@ class ProcimgWriter(Thread):
             finally:
                 # Verzögerte Events prüfen
                 if self.__eventwork:
-                    for tup_fire in list(self.__dict_delay.keys()):
+                    for tup_fire in tuple(self.__dict_delay.keys()):
                         if tup_fire[0].overwrite and \
                                 getattr(self._modio.io, tup_fire[1]).value != \
                                 tup_fire[2]:
diff --git a/revpimodio2/io.py b/revpimodio2/io.py
index 839efe3..05adbbd 100644
--- a/revpimodio2/io.py
+++ b/revpimodio2/io.py
@@ -377,8 +377,9 @@ class IOBase(object):
             )
 
         if self not in self._parentdevice._dict_events:
-            self._parentdevice._dict_events[self] = \
-                [IOEvent(func, edge, as_thread, delay, overwrite)]
+            with self._parentdevice._filelock:
+                self._parentdevice._dict_events[self] = \
+                    [IOEvent(func, edge, as_thread, delay, overwrite)]
         else:
             # Prüfen ob Funktion schon registriert ist
             for regfunc in self._parentdevice._dict_events[self]:
@@ -410,9 +411,10 @@ class IOBase(object):
                     )
 
             # Eventfunktion einfügen
-            self._parentdevice._dict_events[self].append(
-                IOEvent(func, edge, as_thread, delay, overwrite)
-            )
+            with self._parentdevice._filelock:
+                self._parentdevice._dict_events[self].append(
+                    IOEvent(func, edge, as_thread, delay, overwrite)
+                )
 
     def _get_address(self):
         """Gibt die absolute Byteadresse im Prozessabbild zurueck.
@@ -619,7 +621,8 @@ class IOBase(object):
         """
         if self in self._parentdevice._dict_events:
             if func is None:
-                del self._parentdevice._dict_events[self]
+                with self._parentdevice._filelock:
+                    del self._parentdevice._dict_events[self]
             else:
                 newlist = []
                 for regfunc in self._parentdevice._dict_events[self]:
@@ -629,10 +632,11 @@ class IOBase(object):
                         newlist.append(regfunc)
 
                 # Wenn Funktionen übrig bleiben, diese übernehmen
-                if len(newlist) > 0:
-                    self._parentdevice._dict_events[self] = newlist
-                else:
-                    del self._parentdevice._dict_events[self]
+                with self._parentdevice._filelock:
+                    if len(newlist) > 0:
+                        self._parentdevice._dict_events[self] = newlist
+                    else:
+                        del self._parentdevice._dict_events[self]
 
     def wait(self, edge=BOTH, exitevent=None, okvalue=None, timeout=0):
         """Wartet auf Wertaenderung eines IOs.
diff --git a/revpimodio2/modio.py b/revpimodio2/modio.py
index 737ac5b..a871ef2 100644
--- a/revpimodio2/modio.py
+++ b/revpimodio2/modio.py
@@ -312,7 +312,7 @@ class RevPiModIO(object):
         @param milliseconds <class 'int'> in Millisekunden"""
         if self._looprunning:
             raise RuntimeError(
-                "can not change cycletime when cycleloop or mainloop are "
+                "can not change cycletime when cycleloop or mainloop is "
                 "running"
             )
         else:
@@ -580,9 +580,8 @@ class RevPiModIO(object):
 
         # Beim Eintritt in mainloop Bytecopy erstellen
         for dev in self._lst_refresh:
-            dev._filelock.acquire()
-            dev._ba_datacp = dev._ba_devdata[:]
-            dev._filelock.release()
+            with dev._filelock:
+                dev._ba_datacp = dev._ba_devdata[:]
 
         # ImgWriter mit Eventüberwachung aktivieren
         self._imgwriter._collect_events(True)