diff --git a/gearslip/src/main/java/app/seb3thehacker/gearslip/stats/UsageStats.kt b/gearslip/src/main/java/app/seb3thehacker/gearslip/stats/UsageStats.kt
index c9374e9..b5f2b59 100644
--- a/gearslip/src/main/java/app/seb3thehacker/gearslip/stats/UsageStats.kt
+++ b/gearslip/src/main/java/app/seb3thehacker/gearslip/stats/UsageStats.kt
@@ -226,11 +226,11 @@ object UsageStats {
      * build names, not confirmed on a real phone.
      */
     fun osName(context: Context): String {
-        fun installed(pkg: String) = runCatching { context.packageManager.getPackageInfo(pkg, 0) }.isSuccess
+        fun installed(pkg: String) = installed(context, pkg)
         val names = listOf("ro.build.flavor", "ro.build.display.id", "ro.lineage.version")
             .joinToString(" ") { prop(it) } + " " + Build.DISPLAY + " " + Build.FINGERPRINT
         return when {
-            installed("app.grapheneos.setupwizard") -> "GrapheneOS"
+            isGrapheneOs(context) -> "GrapheneOS"
             prop("ro.calyxos.version").isNotEmpty() -> "CalyxOS"
             installed("foundation.e.apps") -> "/e/OS"
             names.contains("iode", ignoreCase = true) -> "iodéOS"
@@ -240,6 +240,12 @@ object UsageStats {
         }
     }
 
+    /** GrapheneOS, told apart from stock Pixel firmware by its own setup app. */
+    fun isGrapheneOs(context: Context) = installed(context, "app.grapheneos.setupwizard")
+
+    private fun installed(context: Context, pkg: String) =
+        runCatching { context.packageManager.getPackageInfo(pkg, 0) }.isSuccess
+
     /** A system property, or "" when it isn't set or can't be read. */
     private fun prop(name: String): String = runCatching {
         Class.forName("android.os.SystemProperties").getMethod("get", String::class.java)
diff --git a/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HelpScreen.kt b/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HelpScreen.kt
index c56414d..9136a96 100644
--- a/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HelpScreen.kt
+++ b/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HelpScreen.kt
@@ -5,6 +5,7 @@ import androidx.compose.ui.res.stringResource
 import app.seb3thehacker.gearslip.R
 import app.seb3thehacker.gearslip.BuildConfig
 import app.seb3thehacker.gearslip.car.CarSettings
+import app.seb3thehacker.gearslip.stats.UsageStats
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.Row
@@ -59,11 +60,13 @@ private val FIRST_DRIVE = listOf(
     ),
 )
 
-private fun inTheCar(onRequestCallScreening: () -> Unit) = listOf(
+private fun inTheCar(grapheneOs: Boolean, onRequestCallScreening: () -> Unit) = listOfNotNull(
     Step(
         R.string.help_plug_in,
         R.string.help_plug_in_detail,
     ),
+    // GrapheneOS can turn off data on the USB port, and then the car never sees the phone (#71).
+    if (grapheneOs) Step(R.string.help_usb_data, R.string.help_usb_data_detail) else null,
     Step(
         R.string.help_pair,
         R.string.help_pair_detail,
@@ -93,9 +96,9 @@ private val USB_AUDIO = listOf(
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun HelpScreen(onBack: () -> Unit, onRequestCallScreening: () -> Unit) {
-    val car = remember(onRequestCallScreening) { inTheCar(onRequestCallScreening) }
-    val usb by CarSettings.pipeAudio.collectAsState()
     val context = LocalContext.current
+    val car = remember(onRequestCallScreening) { inTheCar(UsageStats.isGrapheneOs(context), onRequestCallScreening) }
+    val usb by CarSettings.pipeAudio.collectAsState()
 
     Scaffold(
         containerColor = MaterialTheme.colorScheme.background,
diff --git a/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HomeScreen.kt b/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HomeScreen.kt
index fc36ecd..20ffd8c 100644
--- a/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HomeScreen.kt
+++ b/gearslip/src/main/java/app/seb3thehacker/gearslip/ui/HomeScreen.kt
@@ -25,6 +25,15 @@ import app.seb3thehacker.gearslip.car.CarSettings
 import app.seb3thehacker.gearslip.car.BluetoothAudioCheck
 import android.provider.Settings
 import android.content.Intent
+import android.content.BroadcastReceiver
+import android.content.IntentFilter
+import android.os.BatteryManager
+import androidx.compose.runtime.DisposableEffect
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import app.seb3thehacker.gearslip.stats.UsageStats
+import kotlinx.coroutines.delay
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
 import androidx.compose.material.icons.Icons
@@ -258,6 +267,9 @@ private fun StatusCard(status: SessionStatus.Snapshot) {
     }
 
     val live = status.phase == SessionStatus.Phase.CONNECTING || status.phase == SessionStatus.Phase.PROJECTING
+    val context = LocalContext.current
+    val grapheneOs = remember { UsageStats.isGrapheneOs(context) }
+    val noCar = chargingWithNoCar(status.phase == SessionStatus.Phase.IDLE)
     Surface(color = container, contentColor = content, shape = MaterialTheme.shapes.extraLarge) {
       Column(Modifier.fillMaxWidth().padding(24.dp)) {
         Row(
@@ -286,7 +298,13 @@ private fun StatusCard(status: SessionStatus.Snapshot) {
                     SessionStatus.Phase.FAILED -> status.headline
                 }
                 val detail = when (status.phase) {
-                    SessionStatus.Phase.IDLE -> stringResource(R.string.status_idle_detail)
+                    SessionStatus.Phase.IDLE -> stringResource(
+                        when {
+                            !noCar -> R.string.status_idle_detail
+                            grapheneOs -> R.string.status_no_car_graphene
+                            else -> R.string.status_no_car
+                        },
+                    )
                     SessionStatus.Phase.PROJECTING -> stringResource(R.string.status_projecting_detail)
                     SessionStatus.Phase.DISCONNECTED -> stringResource(R.string.status_disconnected_detail)
                     else -> status.detail
@@ -296,6 +314,13 @@ private fun StatusCard(status: SessionStatus.Snapshot) {
                 Text(detail, style = MaterialTheme.typography.bodyMedium)
             }
         }
+        // GrapheneOS keeps its USB-C port setting under Security & privacy.
+        if (noCar && grapheneOs) {
+            Spacer(Modifier.height(12.dp))
+            Button(onClick = {
+                runCatching { context.startActivity(Intent(Settings.ACTION_SECURITY_SETTINGS)) }
+            }) { Text(stringResource(R.string.status_open_settings)) }
+        }
         // The other way in: wireless, right under the cable's instructions.
         if (!live) {
             Spacer(Modifier.height(20.dp))
@@ -305,6 +330,37 @@ private fun StatusCard(status: SessionStatus.Snapshot) {
     }
 }
 
+/**
+ * True once the phone has charged over a cable for [NO_CAR_MS] while Gearslip sat idle. With
+ * USB data blocked, by a charge-only cable or GrapheneOS's port setting, Android never tells
+ * Gearslip a car is there, so charging with no car is the only sign there is. A wall charger
+ * looks the same, which is why the hint only asks the driver to check.
+ */
+@Composable
+private fun chargingWithNoCar(idle: Boolean): Boolean {
+    val context = LocalContext.current
+    var plugged by remember { mutableStateOf(false) }
+    DisposableEffect(context) {
+        val receiver = object : BroadcastReceiver() {
+            override fun onReceive(c: Context, intent: Intent) {
+                val how = intent.getIntExtra(BatteryManager.EXTRA_PLUGGED, 0)
+                plugged = how == BatteryManager.BATTERY_PLUGGED_USB || how == BatteryManager.BATTERY_PLUGGED_AC
+            }
+        }
+        // The battery broadcast is sticky, so registering hands back the current state at once.
+        context.registerReceiver(receiver, IntentFilter(Intent.ACTION_BATTERY_CHANGED))?.let { receiver.onReceive(context, it) }
+        onDispose { context.unregisterReceiver(receiver) }
+    }
+    var waited by remember { mutableStateOf(false) }
+    LaunchedEffect(idle && plugged) {
+        waited = false
+        if (idle && plugged) { delay(NO_CAR_MS); waited = true }
+    }
+    return idle && plugged && waited
+}
+
+private const val NO_CAR_MS = 10_000L
+
 /** The version shown on screen, straight from the manifest - one place to bump per release. */
 private fun Context.appVersionName(): String =
     runCatching { packageManager.getPackageInfo(packageName, 0).versionName }.getOrNull() ?: "?"
diff --git a/gearslip/src/main/res/values/strings.xml b/gearslip/src/main/res/values/strings.xml
index 9fa6e27..774dc14 100644
--- a/gearslip/src/main/res/values/strings.xml
+++ b/gearslip/src/main/res/values/strings.xml
@@ -269,6 +269,8 @@
     <string name="help_mic_detail">Android won\'t let an app pass music to the car without it. Gearslip listens only when you tap the mic or press the talk button on your wheel.</string>
     <string name="help_plug_in">Plug in, or connect wirelessly.</string>
     <string name="help_plug_in_detail">Gearslip opens by itself when the car connects. For wireless, pair the phone with the car first, then tap Connect wirelessly on Home.</string>
+    <string name="help_usb_data">Allow USB data.</string>
+    <string name="help_usb_data_detail">GrapheneOS can block data on the USB port. If USB-C port control is set to Charging-only, the car never sees the phone, even with a data cable. Set it to allow data.</string>
     <string name="help_pair">Pair over Bluetooth for calls.</string>
     <string name="help_pair_detail">Calls play through the car once your phone and the car are paired. Gearslip offers to pair the first time you plug in.</string>
     <string name="help_answer">Answer calls from the car screen.</string>
@@ -858,6 +860,9 @@
     <!-- Connection status on Home -->
     <string name="status_idle">Not connected</string>
     <string name="status_idle_detail">Plug into the car\'s USB port, or connect wirelessly. Gearslip opens by itself when the car answers.</string>
+    <string name="status_no_car">The phone is charging, but no car has answered. Some cables only charge; try one that carries data.</string>
+    <string name="status_no_car_graphene">The phone is charging, but no car has answered. Check that USB-C port control, under Security &amp; privacy, allows data and isn\'t set to Charging-only.</string>
+    <string name="status_open_settings">Open settings</string>
     <string name="status_connecting">Connecting</string>
     <string name="status_projecting">Projecting</string>
     <string name="status_projecting_detail">Streaming to the head unit.</string>