diff --git a/app/src/main/java/se/ajpanton/notificationsmaster/alerts/AlertPlaybackController.kt b/app/src/main/java/se/ajpanton/notificationsmaster/alerts/AlertPlaybackController.kt
new file mode 100644
index 0000000..e7aaafe
--- /dev/null
+++ b/app/src/main/java/se/ajpanton/notificationsmaster/alerts/AlertPlaybackController.kt
@@ -0,0 +1,49 @@
+package se.ajpanton.notificationsmaster.alerts
+
+/** Plays one resolved effect and invokes [onFinished] when all of its effects finish. */
+fun interface AlertEffectPlayer {
+    fun play(alert: QueuedAlert, onFinished: () -> Unit)
+
+    fun stop() {}
+}
+
+/** Serializes effect playback around the pure queue policy. */
+class AlertPlaybackController(
+    private val effectPlayer: AlertEffectPlayer,
+    private val settings: () -> AlertQueueSettings,
+) {
+    private var queue = AlertQueue()
+
+    @Synchronized
+    fun enqueue(alert: QueuedAlert): AlertQueueTransition {
+        val before = queue
+        return AlertQueueController.enqueue(queue, alert, settings()).also { transition ->
+            queue = transition.queue
+            playCurrentIfChanged(before.current)
+        }
+    }
+
+    @Synchronized
+    fun currentQueue() = queue
+
+    @Synchronized
+    fun stop() {
+        queue = AlertQueue()
+        effectPlayer.stop()
+    }
+
+    @Synchronized
+    private fun complete(alert: QueuedAlert) {
+        if (queue.current != alert) return
+        val before = queue
+        queue = AlertQueueController.completeCurrent(queue).queue
+        playCurrentIfChanged(before.current)
+    }
+
+    private fun playCurrentIfChanged(previous: QueuedAlert?) {
+        val current = queue.current
+        if (previous == current) return
+        effectPlayer.stop()
+        current?.let { alert -> effectPlayer.play(alert) { complete(alert) } }
+    }
+}
diff --git a/app/src/test/java/se/ajpanton/notificationsmaster/alerts/AlertPlaybackControllerTest.kt b/app/src/test/java/se/ajpanton/notificationsmaster/alerts/AlertPlaybackControllerTest.kt
new file mode 100644
index 0000000..4a7eae4
--- /dev/null
+++ b/app/src/test/java/se/ajpanton/notificationsmaster/alerts/AlertPlaybackControllerTest.kt
@@ -0,0 +1,80 @@
+package se.ajpanton.notificationsmaster.alerts
+
+import org.junit.Assert.assertEquals
+import org.junit.Test
+
+class AlertPlaybackControllerTest {
+    private val effects = FakeEffects()
+    private val controller = AlertPlaybackController(effects) { AlertQueueSettings() }
+
+    @Test
+    fun replacementStopsCurrentAndStartsIncomingAlert() {
+        val first = alert("first")
+        val second = alert("second")
+
+        controller.enqueue(first)
+        controller.enqueue(second)
+
+        assertEquals(listOf("first", "second"), effects.played)
+        assertEquals(2, effects.stopCalls)
+    }
+
+    @Test
+    fun protectedCurrentContinuesWhileIncomingAlertWaits() {
+        val current = alert("current", protected = true)
+        val incoming = alert("incoming")
+
+        controller.enqueue(current)
+        controller.enqueue(incoming)
+
+        assertEquals(listOf("current"), effects.played)
+        assertEquals(listOf("current", "incoming"), controller.currentQueue().alerts.map { it.ruleId })
+    }
+
+    @Test
+    fun completionStartsTheNextWaitingAlert() {
+        val current = alert("current", protected = true)
+        val incoming = alert("incoming")
+        controller.enqueue(current)
+        controller.enqueue(incoming)
+
+        effects.finish("current")
+
+        assertEquals(listOf("current", "incoming"), effects.played)
+        assertEquals(listOf("incoming"), controller.currentQueue().alerts.map { it.ruleId })
+    }
+
+    @Test
+    fun staleCompletionCannotAdvanceReplacement() {
+        val first = alert("first")
+        controller.enqueue(first)
+        val staleCompletion = effects.callbacks.getValue("first")
+        controller.enqueue(alert("second"))
+
+        staleCompletion()
+
+        assertEquals(listOf("second"), controller.currentQueue().alerts.map { it.ruleId })
+    }
+
+    private fun alert(id: String, protected: Boolean = false) = QueuedAlert(
+        id,
+        AlertSnapshot("content://" + id, emptyList(), protected, false),
+    )
+
+    private class FakeEffects : AlertEffectPlayer {
+        val played = mutableListOf<String>()
+        val callbacks = mutableMapOf<String, () -> Unit>()
+        var stopCalls = 0
+
+        override fun play(alert: QueuedAlert, onFinished: () -> Unit) {
+            played += alert.ruleId
+            callbacks[alert.ruleId] = onFinished
+        }
+
+        override fun stop() {
+            stopCalls++
+        }
+
+        fun finish(ruleId: String) = callbacks.getValue(ruleId).invoke()
+    }
+}