diff --git a/src/main.cpp b/src/main.cpp
index 60d93d8..82d1d24 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -23,6 +23,7 @@ static PowerService* power;
 static ClockService* clockService;
 
 static String lastKey = "-";
+static String typed;  // last characters typed, for the FORMAT confirmation
 static String lastEvent = "-";
 static bool dirty = true;
 
@@ -55,7 +56,7 @@ static void draw() {
     line("Key: " + lastKey);
     line("Event: " + lastEvent);
     d.setTextColor(TFT_DARKGREY);
-    line("+/- brightness, d: dim test (5s/10s)");
+    line(storage->formatting() ? "Formatting SD card..." : "+/- bright, d: dim test, FORMAT+enter: wipe SD");
 }
 
 static void logEvent(const String& text) {
@@ -103,6 +104,14 @@ static void handleKeys() {
               (state.enter ? " enter" : "") + (state.del ? " del" : "");
     dirty = true;
 
+    if (state.enter) {
+        if (typed.endsWith("FORMAT") && storage->requestFormat()) logEvent("format requested");
+        typed = "";
+    } else {
+        typed += word;
+        if (typed.length() > 16) typed.remove(0, typed.length() - 16);
+    }
+
     int brightness = settings.getInt(Setting::Brightness);
     if (word == "=" || word == "+") settings.setInt(Setting::Brightness, brightness + 10);
     if (word == "-") settings.setInt(Setting::Brightness, brightness - 10);
diff --git a/src/services/storage_service.cpp b/src/services/storage_service.cpp
index 8a4354b..08ed21c 100644
--- a/src/services/storage_service.cpp
+++ b/src/services/storage_service.cpp
@@ -1,6 +1,10 @@
 #include "storage_service.h"
 
 #include <SD.h>
+#include <ff.h>
+#include <sd_diskio.h>
+
+#include <memory>
 
 #include "platform/pins.h"
 #include "platform/shared_spi.h"
@@ -31,11 +35,43 @@ StorageState StorageService::state() const {
 void StorageService::taskEntry(void* self) {
     auto* service = static_cast<StorageService*>(self);
     for (;;) {
+        if (service->formatRequested_) {
+            service->format();
+            service->formatRequested_ = false;
+        }
         service->poll();
-        vTaskDelay(pdMS_TO_TICKS(kPollMs));
+        // Sleep until the next poll, or until a format request wakes us early.
+        ulTaskNotifyTake(pdTRUE, pdMS_TO_TICKS(kPollMs));
     }
 }
 
+bool StorageService::requestFormat() {
+    if (formatRequested_ || !task_) return false;
+    formatRequested_ = true;
+    xTaskNotifyGive(task_);
+    return true;
+}
+
+void StorageService::format() {
+    if (mounted_) SD.end();
+    mounted_ = false;
+
+    bool ok = false;
+    uint8_t pdrv = sdcard_init(pins::kSdCs, &sharedSpi(), 20000000);
+    if (pdrv != 0xFF) {
+        constexpr size_t kWorkSize = 4096;  // FF_MAX_SS
+        std::unique_ptr<uint8_t[]> work(new uint8_t[kWorkSize]);
+        LBA_t partitions[] = {100, 0};  // one partition, 100 % of the card
+        char drive[3] = {static_cast<char>('0' + pdrv), ':', 0};
+        MKFS_PARM options = {FM_FAT32, 0, 0, 0, 0};
+        ok = f_fdisk(pdrv, partitions, work.get()) == FR_OK &&
+             f_mkfs(drive, &options, work.get(), kWorkSize) == FR_OK;
+        sdcard_uninit(pdrv);
+    }
+    bus_.publish(Event::withText(EventType::Notification, ok ? "SD card formatted" : "SD card format failed",
+                                 static_cast<int32_t>(ok ? NotificationLevel::Info : NotificationLevel::Warning)));
+}
+
 bool StorageService::mount() {
     return SD.begin(pins::kSdCs, sharedSpi(), 20000000, "/sd", 5, false);
 }
diff --git a/src/services/storage_service.h b/src/services/storage_service.h
index bcfc39c..b3caa9a 100644
--- a/src/services/storage_service.h
+++ b/src/services/storage_service.h
@@ -12,21 +12,29 @@ namespace roro {
 // Runs on its own task: a failed mount blocks for seconds and must never stall the UI.
 class StorageService : public Service {
    public:
-    explicit StorageService(EventBus& bus) : monitor_(bus) {}
+    explicit StorageService(EventBus& bus) : monitor_(bus), bus_(bus) {}
     const char* name() const override { return "storage"; }
     void start() override;
     void stop() override;
 
     StorageState state() const;
 
+    // Erases the whole card: one partition spanning the card, formatted FAT32. Runs on the storage
+    // task; the result arrives as a Notification. Returns false if a format is already pending.
+    bool requestFormat();
+    bool formatting() const { return formatRequested_; }
+
    private:
     static constexpr uint32_t kPollMs = 15000;
     static void taskEntry(void* self);
     void poll();
     bool mount();
+    void format();
 
     StorageMonitor monitor_;
     bool mounted_ = false;
+    EventBus& bus_;
+    volatile bool formatRequested_ = false;
     TaskHandle_t task_ = nullptr;
     mutable SemaphoreHandle_t lock_ = nullptr;
 };