diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,11 @@
+reactive-banana-automation (0.5.0) upstream; urgency=medium
+
+  * Remove onEvent, which allowed arbitrary IO not connected with
+    actuators, and so was not good for testing. (API change)
+  * Add actuateEvent.
+
+ -- Joey Hess <id@joeyh.name>  Tue, 22 May 2018 17:25:45 -0400
+
 reactive-banana-automation (0.4.0) upstream; urgency=medium
 
   * Simplified using ReaderT, so sensors and actuators do not need to be
diff --git a/Reactive/Banana/Automation.hs b/Reactive/Banana/Automation.hs
--- a/Reactive/Banana/Automation.hs
+++ b/Reactive/Banana/Automation.hs
@@ -26,7 +26,6 @@
 	fromEventSource,
 	gotEvent,
 	getEventFrom,
-	onEvent,
 	-- * Sensors
 	Sensed (..),
 	sensedEvent,
@@ -48,6 +47,7 @@
 	clockSignalBehavior,
 	-- * Actuators
 	PowerChange(..),
+	actuateEvent,
 	actuateBehavior,
 	actuateBehaviorMaybe,
 	-- * Ranges
@@ -114,9 +114,11 @@
 instance Monad (Automation sensors actuators) where
 	return  = Automation . return
 	m >>= g = Automation $ unAutomation m >>= unAutomation . g
+
 instance Applicative (Automation sensors actuators) where
 	pure = Automation . pure
 	f <*> a = Automation $ unAutomation f <*> unAutomation a
+
 instance MonadFix (Automation sensors actuators) where
 	mfix f = Automation $ mfix (unAutomation . f)
 
@@ -223,10 +225,6 @@
 	sensor <- getsensor . fst <$> ask
 	lift $ fromAddHandler $ addHandler sensor
 
--- | Runs an action when an event occurs.
-onEvent :: Event a -> (a -> IO ()) -> Automation sensors actuators ()
-onEvent e a = Automation . lift . reactimate $ fmap a e
-
 -- | A value read from a sensor.
 --
 -- Sensors are sometimes not available, or have not provided a value
@@ -378,6 +376,12 @@
 -- their power turned on and off.
 data PowerChange = PowerOff | PowerOn
 	deriving (Show)
+
+-- | Makes an Event drive an actuator.
+actuateEvent :: Event a -> (a -> actuators) -> Automation sensors actuators ()
+actuateEvent e getactuator = Automation $ do
+	actuators <- snd <$> ask
+	lift $ reactimate $ fmap (actuators . getactuator) e
 
 -- | Makes a Behavior drive an actuator. This will happen when the
 -- Behavior's value changes, but possibly more often as well, depending on
diff --git a/reactive-banana-automation.cabal b/reactive-banana-automation.cabal
--- a/reactive-banana-automation.cabal
+++ b/reactive-banana-automation.cabal
@@ -1,5 +1,5 @@
 Name: reactive-banana-automation
-Version: 0.4.0
+Version: 0.5.0
 Cabal-Version: >= 1.8
 License: AGPL-3
 Maintainer: Joey Hess <id@joeyh.name>