diff --git a/android/app/src/main/java/com/metallic/chiaki/common/RegisteredHost.kt b/android/app/src/main/java/com/metallic/chiaki/common/RegisteredHost.kt
index ea161bc..0acd10f 100644
--- a/android/app/src/main/java/com/metallic/chiaki/common/RegisteredHost.kt
+++ b/android/app/src/main/java/com/metallic/chiaki/common/RegisteredHost.kt
@@ -20,6 +20,7 @@ package com.metallic.chiaki.common
 import androidx.room.*
 import androidx.room.ColumnInfo.BLOB
 import com.metallic.chiaki.lib.RegistHost
+import io.reactivex.Completable
 import io.reactivex.Flowable
 import io.reactivex.Maybe
 import io.reactivex.Single
@@ -61,6 +62,9 @@ interface RegisteredHostDao
 	@Query("SELECT * FROM registered_host WHERE ps4_mac == :mac LIMIT 1")
 	fun getByMac(mac: MacAddress): Maybe<RegisteredHost>
 
+	@Query("DELETE FROM registered_host WHERE ps4_mac == :mac")
+	fun deleteByMac(mac: MacAddress): Completable
+
 	@Insert
 	fun insert(host: RegisteredHost): Single<Long>
 }
\ No newline at end of file
diff --git a/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteActivity.kt b/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteActivity.kt
index 7cd9559..6de946c 100644
--- a/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteActivity.kt
+++ b/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteActivity.kt
@@ -18,6 +18,8 @@
 package com.metallic.chiaki.regist
 
 import android.app.Activity
+import android.app.AlertDialog
+import android.content.DialogInterface
 import android.content.Intent
 import android.os.Bundle
 import android.text.method.ScrollingMovementMethod
@@ -26,6 +28,7 @@ import androidx.appcompat.app.AppCompatActivity
 import androidx.lifecycle.Observer
 import androidx.lifecycle.ViewModelProviders
 import com.metallic.chiaki.R
+import com.metallic.chiaki.common.MacAddress
 import com.metallic.chiaki.common.ext.viewModelFactory
 import com.metallic.chiaki.common.getDatabase
 import com.metallic.chiaki.lib.RegistInfo
@@ -70,11 +73,13 @@ class RegistExecuteActivity: AppCompatActivity()
 					infoTextView.setText(R.string.regist_info_failed)
 					setResult(RESULT_FAILED)
 				}
-				RegistExecuteViewModel.State.SUCCESSFUL ->
+				RegistExecuteViewModel.State.SUCCESSFUL, RegistExecuteViewModel.State.SUCCESSFUL_DUPLICATE ->
 				{
 					infoTextView.visibility = View.VISIBLE
 					infoTextView.setText(R.string.regist_info_success)
 					setResult(RESULT_OK)
+					if(it == RegistExecuteViewModel.State.SUCCESSFUL_DUPLICATE)
+						showDuplicateDialog()
 				}
 				RegistExecuteViewModel.State.STOPPED ->
 				{
@@ -108,4 +113,24 @@ class RegistExecuteActivity: AppCompatActivity()
 		super.onStop()
 		viewModel.stop()
 	}
+
+	private var dialog: AlertDialog? = null
+
+	private fun showDuplicateDialog()
+	{
+		if(dialog != null)
+			return
+
+		val macStr = viewModel.host?.ps4Mac?.let { MacAddress(it).toString() } ?: ""
+
+		dialog = AlertDialog.Builder(this)
+			.setMessage(getString(R.string.alert_regist_duplicate, macStr))
+			.setNegativeButton(R.string.action_regist_discard) { _, _ ->  }
+			.setPositiveButton(R.string.action_regist_overwrite) { _, _ ->
+				viewModel.saveHost()
+			}
+			.create()
+			.also { it.show() }
+
+	}
 }
\ No newline at end of file
diff --git a/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteViewModel.kt b/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteViewModel.kt
index 0173e9d..eaaa947 100644
--- a/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteViewModel.kt
+++ b/android/app/src/main/java/com/metallic/chiaki/regist/RegistExecuteViewModel.kt
@@ -18,7 +18,6 @@
 package com.metallic.chiaki.regist
 
 import android.util.Log
-import androidx.lifecycle.AndroidViewModel
 import androidx.lifecycle.LiveData
 import androidx.lifecycle.MutableLiveData
 import androidx.lifecycle.ViewModel
@@ -29,6 +28,7 @@ import com.metallic.chiaki.common.ext.toLiveData
 import com.metallic.chiaki.lib.*
 import io.reactivex.android.schedulers.AndroidSchedulers
 import io.reactivex.disposables.CompositeDisposable
+import io.reactivex.functions.Action
 import io.reactivex.rxkotlin.addTo
 import io.reactivex.schedulers.Schedulers
 
@@ -40,7 +40,8 @@ class RegistExecuteViewModel(val database: AppDatabase): ViewModel()
 		RUNNING,
 		STOPPED,
 		FAILED,
-		SUCCESSFUL
+		SUCCESSFUL,
+		SUCCESSFUL_DUPLICATE,
 	}
 
 	private val _state = MutableLiveData<State>(State.IDLE)
@@ -53,6 +54,9 @@ class RegistExecuteViewModel(val database: AppDatabase): ViewModel()
 
 	private val disposable = CompositeDisposable()
 
+	var host: RegistHost? = null
+		private set
+
 	fun start(info: RegistInfo)
 	{
 		if(regist != null)
@@ -86,31 +90,36 @@ class RegistExecuteViewModel(val database: AppDatabase): ViewModel()
 
 	private fun registSuccess(host: RegistHost)
 	{
-		_state.postValue(State.SUCCESSFUL) // TODO: more states
-
-		val dao = database.registeredHostDao()
-
-		val mac = MacAddress(host.ps4Mac)
-
-		//val mac = MacAddress(byteArrayOf(0xc0.toByte(), 0xff.toByte(), 0xff.toByte(), 0xee.toByte(), 0xee.toByte(), 0x42))
-
-		dao.getByMac(mac)
+		this.host = host
+		database.registeredHostDao().getByMac(MacAddress(host.ps4Mac))
 			.subscribeOn(Schedulers.io())
 			.observeOn(AndroidSchedulers.mainThread())
 			.doOnSuccess {
-				// TODO: show dialog
-				Log.i("RegistExecuteViewModel", "already exists")
+				_state.value = State.SUCCESSFUL_DUPLICATE
 			}
 			.doOnComplete {
-				dao.insert(RegisteredHost(host))
-					.subscribeOn(Schedulers.io())
-					.subscribe()
-					.addTo(disposable)
+				saveHost()
 			}
 			.subscribe()
 			.addTo(disposable)
 	}
 
+	fun saveHost()
+	{
+		val host = host ?: return
+		val dao = database.registeredHostDao()
+		val registeredHost = RegisteredHost(host)
+		dao.deleteByMac(registeredHost.ps4Mac)
+			.andThen(dao.insert(registeredHost))
+			.subscribeOn(Schedulers.io())
+			.observeOn(AndroidSchedulers.mainThread())
+			.subscribe { _ ->
+				Log.i("RegistExecute", "Registered Host saved in db")
+				_state.value = State.SUCCESSFUL
+			}
+			.addTo(disposable)
+	}
+
 	override fun onCleared()
 	{
 		super.onCleared()
diff --git a/android/app/src/main/res/layout/activity_regist.xml b/android/app/src/main/res/layout/activity_regist.xml
index 40ac926..fff5cad 100644
--- a/android/app/src/main/res/layout/activity_regist.xml
+++ b/android/app/src/main/res/layout/activity_regist.xml
@@ -126,8 +126,7 @@
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
                     android:inputType="textNoSuggestions|textVisiblePassword"
-                    android:maxLines="1"
-                    android:text="test"/>
+                    android:maxLines="1"/>
             </com.google.android.material.textfield.TextInputLayout>
 
             <com.google.android.material.textview.MaterialTextView
@@ -175,8 +174,7 @@
                     android:layout_width="match_parent"
                     android:layout_height="wrap_content"
                     android:inputType="number"
-                    android:maxLength="8"
-                    android:text="01234567"/>
+                    android:maxLength="8"/>
             </com.google.android.material.textfield.TextInputLayout>
 
             <com.google.android.material.button.MaterialButton
diff --git a/android/app/src/main/res/values/strings.xml b/android/app/src/main/res/values/strings.xml
index 36528ad..99ed915 100644
--- a/android/app/src/main/res/values/strings.xml
+++ b/android/app/src/main/res/values/strings.xml
@@ -35,4 +35,7 @@
     <string name="action_share_log">Share Log</string>
     <string name="regist_info_success">Regist successful.</string>
     <string name="regist_info_failed">Regist failed.</string>
+    <string name="alert_regist_duplicate">The console with MAC %s has already been registered. Should the previous record be overwritten?</string>
+    <string name="action_regist_overwrite">Overwrite</string>
+    <string name="action_regist_discard">Cancel</string>
 </resources>
diff --git a/android/app/src/main/res/values/styles.xml b/android/app/src/main/res/values/styles.xml
index eea547b..b5a09da 100644
--- a/android/app/src/main/res/values/styles.xml
+++ b/android/app/src/main/res/values/styles.xml
@@ -35,7 +35,7 @@
         <item name="android:navigationBarColor">?attr/colorPrimarySurface</item>
         <item name="colorControlNormal">@color/accent</item>
         <item name="colorButtonNormal">@color/accent</item>
-        <item name="android:textAppearanceButton">@style/TextAppearanceButton</item>
+        <item name="android:textAppearanceButton">@style/MageTheme.TextAppearanceButton</item>
         <item name="android:textColor">?attr/colorOnPrimary</item>
 
         <item name="textAppearanceHeadline1">@style/MageTheme.TextAppearanceHeadline1</item>
@@ -47,6 +47,8 @@
 
         <item name="android:windowActivityTransitions">true</item>
         <item name="android:windowDrawsSystemBarBackgrounds">true</item>
+
+        <item name="android:alertDialogTheme">@style/MageTheme.AlertDialog</item>
     </style>
 
     <style name="MageTheme.Translucent" parent="MageTheme">
@@ -57,6 +59,15 @@
         <item name="fontFamily">sans-serif-condensed-light</item>
     </style>
 
+    <style name="MageTheme.AlertDialog" parent="Theme.MaterialComponents.Dialog.Alert">
+        <item name="android:textColorPrimary">@android:color/primary_text_light</item>
+        <item name="materialButtonStyle">@style/MageTheme.AlertDialog.Button</item>
+    </style>
+
+    <style name="MageTheme.AlertDialog.Button" parent="Widget.MaterialComponents.Button.TextButton.Dialog">
+        <item name="android:textColor">@color/accent</item>
+    </style>
+
     <style name="MageTheme.TextInputStyle" parent="Widget.MaterialComponents.TextInputLayout.FilledBox">
         <item name="hintTextColor">?attr/colorAccent</item>
         <item name="boxCornerRadiusTopStart">16dp</item>
@@ -72,7 +83,7 @@
         <item name="iconTint">?attr/colorOnSecondary</item>
     </style>
 
-    <style name="TextAppearanceButton" parent="TextAppearance.MaterialComponents.Button">
+    <style name="MageTheme.TextAppearanceButton" parent="TextAppearance.MaterialComponents.Button">
         <item name="android:textColor">?attr/colorOnSecondary</item>
     </style>