Added 'lock' option

src/.idea/compiler.xml

@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <project version="4">
   <component name="CompilerConfiguration">
-    <bytecodeTargetLevel target="11" />
+    <bytecodeTargetLevel target="1.8" />
   </component>
 </project>

src/.idea/deploymentTargetDropDown.xml

@@ -12,6 +12,6 @@
         </deviceKey>
       </Target>
     </targetSelectedWithDropDown>
-    <timeTargetWasSelectedWithDropDown value="2022-09-27T08:04:37.916029Z" />
+    <timeTargetWasSelectedWithDropDown value="2022-09-29T21:08:01.717115Z" />
   </component>
 </project>

src/.idea/gradle.xml

@@ -7,6 +7,7 @@
         <option name="testRunner" value="GRADLE" />
         <option name="distributionType" value="DEFAULT_WRAPPED" />
         <option name="externalProjectPath" value="$PROJECT_DIR$" />
+        <option name="gradleJvm" value="11" />
         <option name="modules">
           <set>
             <option value="$PROJECT_DIR$" />

src/app/src/main/AndroidManifest.xml

@@ -36,6 +36,19 @@
             </intent-filter>
         </receiver>
 
+        <receiver
+            android:name="AdminReceiver"
+            android:permission="android.permission.BIND_DEVICE_ADMIN"
+            android:exported="true">
+            <meta-data
+                android:name="android.app.device_admin"
+                android:resource="@xml/device_admin"/>
+
+            <intent-filter>
+                <action android:name="android.app.action.DEVICE_ADMIN_ENABLED"/>
+            </intent-filter>
+        </receiver>
+
         <activity
             android:name=".MainActivity"
             android:exported="true">

src/app/src/main/java/com/xfarrow/locatemydevice/AdminReceiver.java

@@ -0,0 +1,6 @@
+package com.xfarrow.locatemydevice;
+
+import android.app.admin.DeviceAdminReceiver;
+
+public class AdminReceiver extends DeviceAdminReceiver {
+}

src/app/src/main/java/com/xfarrow/locatemydevice/MainActivity.java

@@ -6,6 +6,8 @@ import androidx.appcompat.app.AppCompatActivity;
 import androidx.core.app.ActivityCompat;
 
 import android.Manifest;
+import android.app.admin.DevicePolicyManager;
+import android.content.ComponentName;
 import android.content.DialogInterface;
 import android.content.Intent;
 import android.content.pm.PackageManager;
@@ -51,9 +53,18 @@ public class MainActivity extends AppCompatActivity {
                     Utils.PERMISSION_MULTIPLE
             );
         }
+
+        // Request display overlay
         if(!android.provider.Settings.canDrawOverlays(this)) {
             displayDrawOverlayPermissionDialog();
         }
+
+        // Admin permission
+        ComponentName cn = new ComponentName(this, AdminReceiver.class);
+        DevicePolicyManager mgr = (DevicePolicyManager)getSystemService(DEVICE_POLICY_SERVICE);
+        if(!mgr.isAdminActive(cn)){
+            requestAdminPermission(cn);
+        }
     }
 
     @Override
@@ -110,4 +121,12 @@ public class MainActivity extends AppCompatActivity {
         });
         alert.show();
     }
+
+    public void requestAdminPermission(ComponentName cn){
+        Intent intent= new Intent(DevicePolicyManager.ACTION_ADD_DEVICE_ADMIN);
+        intent.putExtra(DevicePolicyManager.EXTRA_DEVICE_ADMIN, cn);
+        intent.putExtra(DevicePolicyManager.EXTRA_ADD_EXPLANATION, "The app requires this" +
+                " permission to provide the 'lock' feature.");
+        startActivity(intent);
+    }
 }

src/app/src/main/java/com/xfarrow/locatemydevice/SmsHandler.java

@@ -1,8 +1,11 @@
 package com.xfarrow.locatemydevice;
 
+import static android.content.Context.DEVICE_POLICY_SERVICE;
+
 import android.Manifest;
 import android.annotation.SuppressLint;
 import android.app.admin.DevicePolicyManager;
+import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
@@ -58,7 +61,9 @@ public class SmsHandler {
                 + "|"
                 + Utils.CALL_ME_OPTION
                 + "|"
-                + Utils.WIFI_OPTION + "((" + Utils.WIFI_ENABLE_SUBOPTION + ")|(" + Utils.WIFI_DISABLE_SUBOPTION + "))?";
+                + Utils.WIFI_OPTION + "((" + Utils.WIFI_ENABLE_SUBOPTION + ")|(" + Utils.WIFI_DISABLE_SUBOPTION + "))?"
+                + "|"
+                + Utils.LOCK_OPTION;
 
         Pattern pattern = Pattern.compile(regexToMatch);
         Matcher matcher = pattern.matcher(message);
@@ -298,5 +303,20 @@ public class SmsHandler {
             Utils.sendSms(smsManager, responseSms.toString(), sender);
         }
 
+        // lock
+        else if(providedOption.equals(Utils.LOCK_OPTION)){
+            StringBuilder responseSms = new StringBuilder();
+
+            DevicePolicyManager mgr = (DevicePolicyManager)context.getSystemService(DEVICE_POLICY_SERVICE);
+            if(!mgr.isAdminActive(new ComponentName(context, AdminReceiver.class))){
+                responseSms.append("No admin permission. Aborted");
+                Utils.sendSms(smsManager, responseSms.toString(), sender);
+                return;
+            }
+            mgr.lockNow();
+            responseSms.append("Locked");
+            Utils.sendSms(smsManager, responseSms.toString(), sender);
+        }
+
     }
 }

src/app/src/main/java/com/xfarrow/locatemydevice/SmsReceiver.java

@@ -11,7 +11,8 @@ import android.widget.Toast;
 
 public class SmsReceiver extends BroadcastReceiver {
     // https://www.vogella.com/tutorials/AndroidBroadcastReceiver/article.html
-    // This method gets fired as soon as it receives an SMS
+    // This method gets fired as soon as it receives an SMS.
+    // Consider using a JobService: https://developer.android.com/topic/performance/vitals/anr#slow_broadcast_receivers
     @Override
     public void onReceive(Context context, Intent intent) {
 

src/app/src/main/java/com/xfarrow/locatemydevice/Utils.java

@@ -17,6 +17,7 @@ public class Utils {
     public static final String BATTERY_OPTION = "battery";
     public static final String CALL_ME_OPTION = "callme";
     public static final String WIFI_OPTION = "wifi";
+    public static final String LOCK_OPTION = "lock";
     public static final String WIFI_ENABLE_SUBOPTION = "-enable";
     public static final String WIFI_DISABLE_SUBOPTION = "-disable";
 

src/app/src/main/res/xml/device_admin.xml

@@ -0,0 +1,7 @@
+<device-admin xmlns:android="http://schemas.android.com/apk/res/android">
+
+    <uses-policies>
+        <force-lock/>
+    </uses-policies>
+
+</device-admin>