diff --git a/.gitignore b/.gitignore
index b420a56885..4b62fc423f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,7 +8,6 @@ gen/
 *.iml
 out
 tests
-lint.xml
 local.properties
 ant.properties
 .DS_Store
diff --git a/lint.xml b/lint.xml
new file mode 100644
index 0000000000..1261b667e7
--- /dev/null
+++ b/lint.xml
@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<lint>
+
+    <!-- L10N errors -->
+    <!-- This is a runtime crash so we don't want to ship with this. -->
+    <issue id="StringFormatMatches" severity="error" />
+
+    <!-- L10N warnings -->
+    <issue id="MissingTranslation" severity="warning" />
+    <issue id="MissingQuantity" severity="warning" />
+    <issue id="ExtraTranslation" severity="warning" />
+    <issue id="ImpliedQuantity" severity="warning" />
+
+</lint>
diff --git a/res/values-cy/strings.xml b/res/values-cy/strings.xml
index 0fb18893df..8ec7115db6 100644
--- a/res/values-cy/strings.xml
+++ b/res/values-cy/strings.xml
@@ -85,7 +85,7 @@
   <!--CommunicationActions-->
   <string name="CommunicationActions_no_browser_found">Heb ganfod porwr gwe.</string>
   <!--ConfirmIdentityDialog-->
-  <string name="ConfirmIdentityDialog_your_safety_number_with_s_has_changed">Mae\'ch rhif diogelwch gyda %1$s wedi newid. Gall hyn olygu bod rhywun yn ceisio ymyrryd a\'ch cyfathrebu, neu bod % ​2$s wedi cael ei ail-osod.</string>
+  <string name="ConfirmIdentityDialog_your_safety_number_with_s_has_changed">Mae\'ch rhif diogelwch gyda %1$s wedi newid. Gall hyn olygu bod rhywun yn ceisio ymyrryd a\'ch cyfathrebu, neu bod %2$s wedi cael ei ail-osod.</string>
   <string name="ConfirmIdentityDialog_you_may_wish_to_verify_your_safety_number_with_this_contact">Efallai yr hoffech wirio\'ch rhif diogelwch gyda\'r cyswllt hwn.</string>
   <string name="ConfirmIdentityDialog_accept">Derbyn</string>
   <!--ContactsCursorLoader-->
@@ -868,10 +868,10 @@ Send neges heb ei ddiogelu?</string>
   <!--unverified safety numbers-->
   <string name="IdentityUtil_unverified_banner_one">Mae\'ch rhif diogelwch gyda %1$s wedi newid ac nid yw wedi\'i dilysu bellach.</string>
   <string name="IdentityUtil_unverified_banner_two">Nid yw eich rhif diogelwch gyda %1$s a %2$s wedi\'i dilysu bellach</string>
-  <string name="IdentityUtil_unverified_banner_many">Nid yw eich rhifau diogelwch gyda %1$s,%2$s, a %3$s bellach yn cael eu gwirio</string>
-  <string name="IdentityUtil_unverified_dialog_one">Mae\'ch rhif diogelwch gyda %1$s wedi newid ac nid yw wedi\'i dilysu bellach. Gall hyn olygu bod rhywun yn ceisio rhyng-gipio eich cyfathrebu, neu bod %​1$s wedi ail-osod Signal.</string>
-  <string name="IdentityUtil_unverified_dialog_two">Nid yw eich rhif diogelwch gyda %1$s wedi\'i dilysu bellach. Gall hyn olygu bod rhywun yn ceisio rhyng-gipio eich cyfathrebu, neu bod %​1$s wedi ail-osod Signal.</string>
-  <string name="IdentityUtil_unverified_dialog_many">Nid yw eich rhifau diogelwch gyda %1$s, %2$s, a %3$s bellach yn cael eu gwirio. Gall hyn olygu bod rhywun yn ceisio rhyng-gipio eich cyfathrebu, neu bod %​1$s wedi ail-osod Signal.</string>
+  <string name="IdentityUtil_unverified_banner_many">Nid yw eich rhifau diogelwch gyda %1$s, %2$s, a %3$s bellach yn cael eu gwirio</string>
+  <string name="IdentityUtil_unverified_dialog_one">Mae\'ch rhif diogelwch gyda %1$s wedi newid ac nid yw wedi\'i dilysu bellach. Gall hyn olygu bod rhywun yn ceisio rhyng-gipio eich cyfathrebu, neu bod %1$s wedi ail-osod Signal.</string>
+  <string name="IdentityUtil_unverified_dialog_two">Mae\'ch rhifau diogelwch gyda %1$s a %2$s wedi\'i dilysu bellach. Gall hyn olygu bod rhywun yn ceisio rhyng-gipio eich cyfathrebu, neu bod nhw wedi ail-osod Signal.</string>
+  <string name="IdentityUtil_unverified_dialog_many">Mae\'ch rhifau diogelwch gyda %1$s, %2$s, a %3$s wedi\'i dilysi bellach. Gall hyn olygu bod rhywun yn ceisio rhyng-gipio eich cyfathrebu, neu bod nhw wedi ail-osod Signal.</string>
   <string name="IdentityUtil_untrusted_dialog_one">Mae\'ch rhif diogelwch gyda %1$s wedi newid yn ddiweddar.</string>
   <string name="IdentityUtil_untrusted_dialog_two">Mae\'ch rhif diogelwch gyda %1$s wedi newid yn ddiweddar.</string>
   <string name="IdentityUtil_untrusted_dialog_many">Mae\'ch rhif diogelwch gyda %1$s a %3$s wedi newid.</string>
diff --git a/res/values/styles.xml b/res/values/styles.xml
index 75d8382c9e..a9aaf9d788 100644
--- a/res/values/styles.xml
+++ b/res/values/styles.xml
@@ -42,7 +42,7 @@
     <style name="TextSecure.DarkActionBar"
            parent="@style/Widget.AppCompat.ActionBar">
         <item name="background">@color/core_grey_90</item>
-        <item name="android:popupTheme">@style/ThemeOverlay.AppCompat.Dark</item>
+        <item name="android:popupTheme" tools:ignore="NewApi">@style/ThemeOverlay.AppCompat.Dark</item>
         <item name="elevation">4dp</item>
         <item name="popupTheme">@style/ThemeOverlay.AppCompat.Dark</item>
         <item name="titleTextStyle">@style/TextSecure.TitleTextStyle</item>
@@ -155,8 +155,8 @@
     </style>
 
     <style name="MaterialButton">
-        <item name="android:elevation">1dp</item>
-        <item name="android:translationZ">1dp</item>
+        <item name="android:elevation" tools:ignore="NewApi">1dp</item>
+        <item name="android:translationZ" tools:ignore="NewApi">1dp</item>
         <item name="android:textColor">@color/white</item>
         <item name="android:textSize">12sp</item>
     </style>
diff --git a/res/values/text_styles.xml b/res/values/text_styles.xml
index c020c7bc9c..544cd22c75 100644
--- a/res/values/text_styles.xml
+++ b/res/values/text_styles.xml
@@ -1,10 +1,10 @@
 <?xml version="1.0" encoding="utf-8"?>
-<resources>
+<resources xmlns:tools="http://schemas.android.com/tools">
     <style name="Signal.Text.Headline" parent="Base.TextAppearance.AppCompat.Headline">
         <item name="android:textSize">28sp</item>
         <item name="android:lineSpacingExtra">3sp</item>
         <item name="android:fontFamily">sans-serif</item>
-        <item name="android:letterSpacing">0</item>
+        <item name="android:letterSpacing" tools:ignore="NewApi">0</item>
     </style>
 
     <style name="Signal.Text.Headline.Registration" parent="Signal.Text.Headline">
@@ -15,21 +15,21 @@
         <item name="android:textSize">16sp</item>
         <item name="android:lineSpacingExtra">4sp</item>
         <item name="android:fontFamily">sans-serif</item>
-        <item name="android:letterSpacing">0.01</item>
+        <item name="android:letterSpacing" tools:ignore="NewApi">0.01</item>
     </style>
 
     <style name="Signal.Text.Preview" parent="Base.TextAppearance.AppCompat.Body2">
         <item name="android:textSize">14sp</item>
         <item name="android:lineSpacingExtra">3sp</item>
         <item name="android:fontFamily">sans-serif</item>
-        <item name="android:letterSpacing">0.01</item>
+        <item name="android:letterSpacing" tools:ignore="NewApi">0.01</item>
     </style>
 
     <style name="Signal.Text.Caption" parent="Base.TextAppearance.AppCompat.Caption">
         <item name="android:textSize">12sp</item>
         <item name="android:lineSpacingExtra">2sp</item>
         <item name="android:fontFamily">sans-serif</item>
-        <item name="android:letterSpacing">0.03</item>
+        <item name="android:letterSpacing" tools:ignore="NewApi">0.03</item>
     </style>
 
 
diff --git a/res/values/themes.xml b/res/values/themes.xml
index f08fd9b7c9..093d7a6139 100644
--- a/res/values/themes.xml
+++ b/res/values/themes.xml
@@ -34,7 +34,7 @@
         <item name="actionBarPopupTheme">@style/ThemeOverlay.AppCompat.Dark</item>
         <item name="colorPrimary">@color/gray95</item>
         <item name="colorAccent">@color/signal_primary_dark</item>
-        <item name="android:colorControlActivated">@color/signal_primary_dark</item>
+        <item name="android:colorControlActivated" tools:ignore="NewApi">@color/signal_primary_dark</item>
 
         <item name="recipient_preference_blocked">#d00000</item>
         <item name="contact_selection_label_text">#66eeeeee</item>
diff --git a/src/org/thoughtcrime/securesms/ConfirmIdentityDialog.java b/src/org/thoughtcrime/securesms/ConfirmIdentityDialog.java
index e8d2bc0f86..1615dee48d 100644
--- a/src/org/thoughtcrime/securesms/ConfirmIdentityDialog.java
+++ b/src/org/thoughtcrime/securesms/ConfirmIdentityDialog.java
@@ -48,7 +48,7 @@ public class ConfirmIdentityDialog extends AlertDialog {
 
       Recipient       recipient       = Recipient.from(context, mismatch.getAddress(), false);
       String          name            = recipient.toShortString();
-      String          introduction    = String.format(context.getString(R.string.ConfirmIdentityDialog_your_safety_number_with_s_has_changed), name, name);
+      String          introduction    = context.getString(R.string.ConfirmIdentityDialog_your_safety_number_with_s_has_changed, name, name);
       SpannableString spannableString = new SpannableString(introduction + " " +
                                                             context.getString(R.string.ConfirmIdentityDialog_you_may_wish_to_verify_your_safety_number_with_this_contact));
 
diff --git a/src/org/thoughtcrime/securesms/audio/AudioSlidePlayer.java b/src/org/thoughtcrime/securesms/audio/AudioSlidePlayer.java
index 66d46dd218..9f939feafc 100644
--- a/src/org/thoughtcrime/securesms/audio/AudioSlidePlayer.java
+++ b/src/org/thoughtcrime/securesms/audio/AudioSlidePlayer.java
@@ -161,7 +161,9 @@ public class AudioSlidePlayer implements SensorEventListener {
               sensorManager.unregisterListener(AudioSlidePlayer.this);
 
               if (wakeLock != null && wakeLock.isHeld()) {
-                wakeLock.release(PowerManager.RELEASE_FLAG_WAIT_FOR_NO_PROXIMITY);
+                if (Build.VERSION.SDK_INT >= 21) {
+                  wakeLock.release(PowerManager.RELEASE_FLAG_WAIT_FOR_NO_PROXIMITY);
+                }
               }
             }
 
@@ -187,7 +189,9 @@ public class AudioSlidePlayer implements SensorEventListener {
           sensorManager.unregisterListener(AudioSlidePlayer.this);
 
           if (wakeLock != null && wakeLock.isHeld()) {
-            wakeLock.release(PowerManager.RELEASE_FLAG_WAIT_FOR_NO_PROXIMITY);
+            if (Build.VERSION.SDK_INT >= 21) {
+              wakeLock.release(PowerManager.RELEASE_FLAG_WAIT_FOR_NO_PROXIMITY);
+            }
           }
         }
 
diff --git a/src/org/thoughtcrime/securesms/mms/LegacyMmsConnection.java b/src/org/thoughtcrime/securesms/mms/LegacyMmsConnection.java
index 1067978b76..7068c3795c 100644
--- a/src/org/thoughtcrime/securesms/mms/LegacyMmsConnection.java
+++ b/src/org/thoughtcrime/securesms/mms/LegacyMmsConnection.java
@@ -16,10 +16,16 @@
  */
 package org.thoughtcrime.securesms.mms;
 
+import android.Manifest;
+import android.annotation.SuppressLint;
 import android.content.Context;
+import android.content.pm.PackageManager;
 import android.net.ConnectivityManager;
+import android.support.annotation.NonNull;
+import android.support.v4.app.ActivityCompat;
 import android.telephony.TelephonyManager;
 import android.text.TextUtils;
+
 import org.thoughtcrime.securesms.logging.Log;
 
 import org.apache.http.Header;
@@ -209,7 +215,7 @@ public abstract class LegacyMmsConnection {
   }
 
   protected List<Header> getBaseHeaders() {
-    final String                number    = TelephonyUtil.getManager(context).getLine1Number(); ;
+    final String number = getLine1Number(context);
 
     return new LinkedList<Header>() {{
       add(new BasicHeader("Accept", "*/*, application/vnd.wap.mms-message, application/vnd.wap.sic"));
@@ -223,6 +229,17 @@ public abstract class LegacyMmsConnection {
     }};
   }
 
+  @SuppressLint("HardwareIds")
+  private static String getLine1Number(@NonNull Context context) {
+    if (ActivityCompat.checkSelfPermission(context, Manifest.permission.READ_SMS)           == PackageManager.PERMISSION_GRANTED ||
+        ActivityCompat.checkSelfPermission(context, Manifest.permission.READ_PHONE_NUMBERS) == PackageManager.PERMISSION_GRANTED ||
+        ActivityCompat.checkSelfPermission(context, Manifest.permission.READ_PHONE_STATE)   == PackageManager.PERMISSION_GRANTED) {
+      return TelephonyUtil.getManager(context).getLine1Number();
+    } else {
+      return "";
+    }
+  }
+
   public static class Apn {
 
     public static Apn EMPTY = new Apn("", "", "", "", "");
diff --git a/src/org/thoughtcrime/securesms/util/IdentityUtil.java b/src/org/thoughtcrime/securesms/util/IdentityUtil.java
index de458f9ce8..89ce2e5996 100644
--- a/src/org/thoughtcrime/securesms/util/IdentityUtil.java
+++ b/src/org/thoughtcrime/securesms/util/IdentityUtil.java
@@ -1,12 +1,10 @@
 package org.thoughtcrime.securesms.util;
 
-import android.annotation.SuppressLint;
 import android.content.Context;
 import android.os.AsyncTask;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.annotation.StringRes;
-import android.support.annotation.UiThread;
 
 import org.thoughtcrime.securesms.R;
 import org.thoughtcrime.securesms.crypto.storage.TextSecureIdentityKeyStore;
@@ -47,8 +45,6 @@ public class IdentityUtil {
 
   private static final String TAG = IdentityUtil.class.getSimpleName();
 
-  @SuppressLint("StaticFieldLeak")
-  @UiThread
   public static ListenableFuture<Optional<IdentityRecord>> getRemoteIdentityKey(final Context context, final Recipient recipient) {
     final SettableFuture<Optional<IdentityRecord>> future = new SettableFuture<>();