diff --git a/firmware/Cargo.lock b/firmware/Cargo.lock
index 877ee56..a5c0826 100644
--- a/firmware/Cargo.lock
+++ b/firmware/Cargo.lock
@@ -306,6 +306,7 @@ dependencies = [
  "rp2040-boot2",
  "rp2040-hal",
  "usb-device",
+ "usbd-serial",
 ]
 
 [[package]]
@@ -645,6 +646,18 @@ dependencies = [
  "portable-atomic",
 ]
 
+[[package]]
+name = "usbd-serial"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "065e4eaf93db81d5adac82d9cef8f8da314cb640fa7f89534b972383f1cf80fc"
+dependencies = [
+ "embedded-hal 0.2.7",
+ "embedded-io",
+ "nb 1.1.0",
+ "usb-device",
+]
+
 [[package]]
 name = "vcell"
 version = "0.1.3"
diff --git a/firmware/Cargo.toml b/firmware/Cargo.toml
index f54d78f..9be6b56 100644
--- a/firmware/Cargo.toml
+++ b/firmware/Cargo.toml
@@ -15,6 +15,7 @@ panic-reset = "0.1"
 rp2040-boot2 = "0.3"
 rp2040-hal = { version = "0.10", features = ["rt", "critical-section-impl"] }
 usb-device = "0.3"
+usbd-serial = "0.2"
 critical-section = { version = "1" }
 
 # Dependencies for debug probe
diff --git a/firmware/src/hid_class.rs b/firmware/src/hid_class.rs
index c19cf0e..dbd2964 100644
--- a/firmware/src/hid_class.rs
+++ b/firmware/src/hid_class.rs
@@ -30,6 +30,27 @@ const HID_DESCRIPTOR: [u8; 7] = [
     DESCRIPTOR_LEN_BYTES[1], // wDescriptorLength - LSB first
 ];
 
+#[derive(Debug, Default, Copy, Clone)]
+pub struct LedState {
+    num_lock: bool,
+    caps_lock: bool,
+    scroll_lock: bool,
+    compose: bool,
+    kana: bool,
+}
+
+impl From<u8> for LedState {
+    fn from(byte: u8) -> Self {
+        Self {
+            num_lock: byte & 1 == 1,
+            caps_lock: (byte >> 1) & 1 == 1,
+            scroll_lock: (byte >> 2) & 1 == 1,
+            compose: (byte >> 3) & 1 == 1,
+            kana: (byte >> 4) & 1 == 1,
+        }
+    }
+}
+
 // A HID device is composed of the following endpoints:
 // * A pair of control IN and OUT endpoints called the default endpoint
 //   (these are handled by usb-device?)
@@ -52,6 +73,9 @@ pub struct HidClass<'a, B: UsbBus> {
     // if declared.
     // out_endpoint: EndpointOut<'a, B>,
     _bus: PhantomData<B>,
+
+    last_report: [u8; 8],
+    led_state: LedState,
 }
 
 impl<'a, B: UsbBus> HidClass<'a, B> {
@@ -64,11 +88,24 @@ impl<'a, B: UsbBus> HidClass<'a, B> {
         let poll_interval = 1;
         let in_endpoint = bus_allocator.interrupt(max_packet_size, poll_interval);
 
-        Self { usb_interface, in_endpoint, _bus: PhantomData {} }
+        let last_report = [0; 8];
+
+        Self {
+            usb_interface,
+            in_endpoint,
+            _bus: PhantomData {},
+            last_report,
+            led_state: LedState::default(),
+        }
+    }
+
+    pub fn write_raw_report(&mut self, data: [u8; 8]) -> Result<usize> {
+        self.last_report = data;
+        self.in_endpoint.write(&data)
     }
 
-    pub fn write_raw_report(&self, data: &[u8]) -> Result<usize> {
-        self.in_endpoint.write(data)
+    pub fn led_state(&self) -> LedState {
+        self.led_state
     }
 }
 
@@ -144,7 +181,25 @@ impl<B: UsbBus> UsbClass<B> for HidClass<'_, B> {
     fn poll(&mut self) {}
 
     fn control_out(&mut self, xfer: ControlOut<B>) {
-        let _ = xfer;
+        const SET_REPORT_REQUEST: u8 = 0x09;
+
+        let request = xfer.request();
+
+        let interface = request.index;
+        if interface != u8::from(self.usb_interface) as u16 {
+            return;
+        }
+
+        if request.request == SET_REPORT_REQUEST {
+            let data_len = xfer.data().len();
+
+            if data_len > 0 {
+                // The keyboard OUT report is 1 byte for the LED state.
+                self.led_state = LedState::from(xfer.data()[0]);
+            }
+
+            xfer.accept().ok();
+        }
     }
 
     // The Control pipe is used for:
@@ -152,6 +207,13 @@ impl<B: UsbBus> UsbClass<B> for HidClass<'_, B> {
     // * Transmitting data when polled by the HID class driver (using the Get_Report request).
     // * Receiving data from the host.
     fn control_in(&mut self, xfer: ControlIn<B>) {
+        const GET_REPORT_REQUEST: u8 = 0x01;
+        // const GET_IDLE_REQUEST: u8 = 0x02;
+        // const GET_PROTOCOL_REQUEST: u8 = 0x03;
+        // const SET_REPORT_REQUEST: u8 = 0x09;
+        // const SET_IDLE_REQUEST: u8 = 0x0A;
+        // const SET_PROTOCOL_REQUEST: u8 = 0x0B;
+
         let request = xfer.request();
 
         let interface = request.index;
@@ -188,7 +250,17 @@ impl<B: UsbBus> UsbClass<B> for HidClass<'_, B> {
                     _ => {},
                 }
             },
-            (RequestType::Class, 0x0) => {},
+            (RequestType::Class, GET_REPORT_REQUEST) => {
+                const REPORT_TYPE_INPUT: u8 = 0x01;
+                // const REPORT_TYPE_OUTPUT: u8 = 0x02;
+                // const REPORT_TYPE_FEATURE: u8 = 0x03;
+
+                let [_report_id, report_type] = request.value.to_le_bytes();
+
+                if report_type == REPORT_TYPE_INPUT {
+                    xfer.accept_with(&self.last_report).ok();
+                }
+            },
             _ => {},
         }
     }
diff --git a/firmware/src/key_codes.rs b/firmware/src/key_codes.rs
index 4bca6b0..da8eb21 100644
--- a/firmware/src/key_codes.rs
+++ b/firmware/src/key_codes.rs
@@ -5,6 +5,7 @@ use defmt::Format;
 #[derive(Copy, Clone, Format, PartialEq)]
 pub enum KeyCode {
     Empty = 0x0,
+    ErrorRollOver = 0x01,
     A = 0x04,
     B = 0x05,
     C = 0x06,
diff --git a/firmware/src/key_scan.rs b/firmware/src/key_scan.rs
index 1dc68e2..b6aa000 100644
--- a/firmware/src/key_scan.rs
+++ b/firmware/src/key_scan.rs
@@ -83,6 +83,10 @@ impl<const NUM_ROWS: usize, const NUM_COLS: usize> From<KeyScan<NUM_ROWS, NUM_CO
             if keycode_index < keycodes.len() {
                 keycodes[keycode_index] = key;
                 keycode_index += 1;
+            } else {
+                for keycode in &mut keycodes {
+                    *keycode = KeyCode::ErrorRollOver as u8;
+                }
             }
         };
 
diff --git a/firmware/src/main.rs b/firmware/src/main.rs
index 8212921..94238ab 100644
--- a/firmware/src/main.rs
+++ b/firmware/src/main.rs
@@ -31,6 +31,7 @@ use rp2040_hal::{
     Clock, Watchdog,
 };
 use usb_device::{bus::UsbBusAllocator, device::UsbDeviceBuilder, prelude::*};
+use usbd_serial::{embedded_io::Write, SerialPort};
 
 /// The rate of polling of the keyboard itself in firmware.
 const SCAN_LOOP_RATE_MS: u32 = 1;
@@ -60,6 +61,9 @@ static mut USB_BUS: Option<UsbBusAllocator<usb::UsbBus>> = None;
 static USB_HID_CLASS: Mutex<RefCell<Option<HidClass<usb::UsbBus>>>> =
     Mutex::new(RefCell::new(None));
 
+static USB_SERIAL_CLASS: Mutex<RefCell<Option<SerialPort<usb::UsbBus>>>> =
+    Mutex::new(RefCell::new(None));
+
 #[defmt::panic_handler]
 fn panic() -> ! {
     cortex_m::asm::udf()
@@ -163,6 +167,7 @@ fn main() -> ! {
     };
 
     let hid_class = HidClass::new(bus_allocator_ref);
+    let serial = SerialPort::new(bus_allocator_ref);
 
     // https://github.com/obdev/v-usb/blob/7a28fdc685952412dad2b8842429127bc1cf9fa7/usbdrv/USB-IDs-for-free.txt#L128
     let keyboard_usb_device = UsbDeviceBuilder::new(bus_allocator_ref, UsbVidPid(0x16c0, 0x27db))
@@ -175,6 +180,7 @@ fn main() -> ! {
         // Note (safety): This is safe as interrupts haven't been started yet
         critical_section::with(|cs| {
             USB_HID_CLASS.replace(cs, Some(hid_class));
+            USB_SERIAL_CLASS.replace(cs, Some(serial));
         });
 
         USB_DEVICE = Some(keyboard_usb_device);
@@ -188,6 +194,9 @@ fn main() -> ! {
     let mut tick_count_down = timer.count_down();
     tick_count_down.start(1.millis());
 
+    let mut print_led_state_count_down = timer.count_down();
+    print_led_state_count_down.start(1.secs());
+
     let mut last_report: KeyboardReport = scan.into();
 
     loop {
@@ -200,7 +209,7 @@ fn main() -> ! {
                     let mut hid_class = USB_HID_CLASS.borrow_ref_mut(cs);
                     let hid_class = hid_class.as_mut().unwrap();
 
-                    if let Err(err) = hid_class.write_raw_report(&report.as_raw_input()) {
+                    if let Err(err) = hid_class.write_raw_report(report.as_raw_input()) {
                         match err {
                             UsbError::WouldBlock => warn!("UsbError::WouldBlock"),
                             UsbError::ParseError => error!("UsbError::ParseError"),
@@ -220,6 +229,20 @@ fn main() -> ! {
                 });
             }
         }
+
+        if print_led_state_count_down.wait().is_ok() {
+            critical_section::with(|cs| {
+                let mut hid_class = USB_HID_CLASS.borrow_ref_mut(cs);
+                let hid_class = hid_class.as_mut().unwrap();
+
+                let mut serial = USB_SERIAL_CLASS.borrow_ref_mut(cs);
+                let serial = serial.as_mut().unwrap();
+
+                let led_state = hid_class.led_state();
+
+                let _ = writeln!(serial, "{led_state:?}");
+            });
+        }
     }
 }
 
@@ -233,6 +256,9 @@ unsafe fn USBCTRL_IRQ() {
         let mut hid_class = USB_HID_CLASS.borrow_ref_mut(cs);
         let hid_class = hid_class.as_mut().unwrap();
 
-        usb_dev.poll(&mut [hid_class]);
+        let mut serial = USB_SERIAL_CLASS.borrow_ref_mut(cs);
+        let serial = serial.as_mut().unwrap();
+
+        usb_dev.poll(&mut [hid_class, serial]);
     });
 }