diff --git a/build.gradle.kts b/build.gradle.kts
index 5959e3ce8..e2e6fc6ea 100644
--- a/build.gradle.kts
+++ b/build.gradle.kts
@@ -22,4 +22,14 @@ plugins {
     alias(libs.plugins.secrets.gradle.plugin) apply false
     alias(libs.plugins.hilt.android) apply false
     alias(libs.plugins.ksp) apply false
-}
\ No newline at end of file
+}
+
+// Share the isCI flag with all subprojects (optional, the script handles it if omitted)
+val isCI = System.getenv("CI")?.toBoolean() ?: false
+extra["isCI"] = isCI
+
+// Enforce that required API keys are present in secrets.properties
+extra["requiredSecrets"] = listOf("MAPS_API_KEY")
+
+// Apply the enforcement script
+apply(from = "gradle/secrets-enforcement.gradle.kts")
\ No newline at end of file
diff --git a/gradle/secrets-enforcement.gradle.kts b/gradle/secrets-enforcement.gradle.kts
new file mode 100644
index 000000000..c2e265da1
--- /dev/null
+++ b/gradle/secrets-enforcement.gradle.kts
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.util.Properties
+
+/**
+ * This script enforces that required API keys are present in a `secrets.properties` file
+ * before allowing build or install tasks to proceed. It ignores syncs and test tasks.
+ *
+ * Usage in build.gradle.kts:
+ *
+ * extra["requiredSecrets"] = listOf("MAPS3D_API_KEY", "PLACES_API_KEY")
+ * apply(from = "gradle/secrets-enforcement.gradle.kts")
+ */
+
+// Use the provided isCI flag if available, otherwise detect it from environment variables
+val isCI = if (project.extra.has("isCI")) {
+    project.extra["isCI"] as? Boolean ?: false
+} else {
+    System.getenv("CI")?.toBoolean() ?: false
+}
+
+if (!isCI) {
+    val secretsFile = rootProject.file("secrets.properties")
+    val requestedTasks = gradle.startParameter.taskNames
+    @Suppress("UNCHECKED_CAST")
+    val requiredKeys = (project.extra["requiredSecrets"] as? List<String>) ?: emptyList()
+
+    if (requestedTasks.isEmpty() && !secretsFile.exists()) {
+        // It's likely an IDE sync if no tasks are specified, so just issue a warning.
+        println("Warning: secrets.properties not found. Gradle sync may succeed, but building/running the app will fail.")
+    } else if (requestedTasks.isNotEmpty()) {
+        val buildTaskKeywords = setOf("build", "install", "assemble")
+        val testTaskKeywords = setOf("test", "report", "lint")
+
+        val isBuildTask = requestedTasks.any { name ->
+            buildTaskKeywords.any { kw -> name.contains(kw, ignoreCase = true) }
+        }
+        val isTestTask = requestedTasks.any { name ->
+            testTaskKeywords.any { kw -> name.contains(kw, ignoreCase = true) }
+        }
+        val isDebugTask = requestedTasks.any { task ->
+            task.contains("Debug", ignoreCase = true) || task.contains("installAndLaunch", ignoreCase = true)
+        }
+
+        if (isBuildTask && !isTestTask && isDebugTask) {
+            val defaultsFile = rootProject.file("local.defaults.properties")
+            val requiredKeysMessage = if (defaultsFile.exists()) {
+                defaultsFile.readText()
+            } else {
+                requiredKeys.joinToString("\n") { "$it=<YOUR_API_KEY>" }
+            }
+
+            if (!secretsFile.exists()) {
+                throw GradleException("secrets.properties file not found. Please create a 'secrets.properties' file in the root project directory with the following content:\n\n$requiredKeysMessage")
+            }
+
+            val secrets = Properties()
+            secretsFile.inputStream().use { secrets.load(it) }
+
+            requiredKeys.forEach { key ->
+                val value = secrets.getProperty(key)
+                if (value.isNullOrBlank() || !value.matches(Regex("^AIza[a-zA-Z0-9_-]{35}$"))) {
+                    throw GradleException("Invalid or missing $key in secrets.properties. Please provide a valid Google API key (starts with 'AIza').")
+                }
+            }
+        }
+    }
+}