diff --git a/src/clock.c b/src/clock.c
index 32e6ff78..09f53d64 100644
--- a/src/clock.c
+++ b/src/clock.c
@@ -51,6 +51,16 @@ void sleep_ticks(uint32_t ticks)
 		;
 }
 
+/**
+ * @brief Sleep (i.e.: do nothing) for a number of seconds.
+ *
+ * @param[in] seconds Sleep duration, in seconds.
+ */
+void sleep_seconds(float seconds)
+{
+	sleep_ticks((uint32_t)(seconds * SYSTICK_FREQUENCY_HZ));
+}
+
 /**
  * @brief Start the stopwatch to measure elapsed time.
  *
diff --git a/src/clock.h b/src/clock.h
index 10298f52..478933be 100644
--- a/src/clock.h
+++ b/src/clock.h
@@ -11,6 +11,7 @@ void each(uint32_t period, void (*function)(void), uint32_t during);
 uint32_t get_clock_ticks(void);
 uint32_t read_cycle_counter(void);
 void sleep_ticks(uint32_t ticks);
+void sleep_seconds(float seconds);
 void stopwatch_start(void);
 float stopwatch_stop(void);
 void sleep_us(uint32_t us);
diff --git a/src/hmi.c b/src/hmi.c
index 895d382a..5317252b 100644
--- a/src/hmi.c
+++ b/src/hmi.c
@@ -110,6 +110,36 @@ void blink_collision(void)
 	led_right_off();
 }
 
+/**
+ * @brief Warn low battery using speaker sounds.
+ */
+void speaker_warn_low_battery(void)
+{
+	speaker_play('C', 4, 0, 0.05);
+	sleep_ticks(50);
+	speaker_play('C', 3, 0, 0.05);
+	sleep_ticks(50);
+}
+
+/**
+ * @brief Notify about an error with a low pitch sustained sound.
+ */
+void speaker_play_error(void)
+{
+	speaker_play('C', 3, 0, 2.);
+}
+
+/**
+ * @brief Play three fast, high tones to note a successful operation.
+ */
+void speaker_play_success(void)
+{
+	for (int i = 0; i < 3; i++) {
+		speaker_play('C', 8, 0, 0.05);
+		sleep_ticks(50);
+	}
+}
+
 /**
  * @brief Function to read button left.
  */
diff --git a/src/hmi.h b/src/hmi.h
index 052a6558..b2bf3e97 100644
--- a/src/hmi.h
+++ b/src/hmi.h
@@ -5,6 +5,7 @@
 
 #include "clock.h"
 #include "detection.h"
+#include "speaker.h"
 #include "speed.h"
 
 void led_left_toggle(void);
@@ -18,6 +19,9 @@ void led_right_off(void);
 void led_bluepill_off(void);
 void repeat_blink(uint8_t count, uint16_t time);
 void blink_collision(void);
+void speaker_warn_low_battery(void);
+void speaker_play_error(void);
+void speaker_play_success(void);
 bool button_left_read(void);
 bool button_right_read(void);
 bool button_left_read_consecutive(uint32_t count);
diff --git a/src/main.c b/src/main.c
index b0ad6956..f7746db0 100644
--- a/src/main.c
+++ b/src/main.c
@@ -12,6 +12,7 @@
 #include "serial.h"
 #include "setup.h"
 #include "solve.h"
+#include "speaker.h"
 #include "speed.h"
 
 static void competition(void);
@@ -46,6 +47,24 @@ static void user_configuration(bool run)
 	set_speed_mode(mode, run);
 }
 
+/**
+ * @brief Check battery voltage and warn if the voltage is getting too low.
+ */
+static void check_battery_voltage(void)
+{
+	float voltage;
+
+	voltage = get_battery_voltage();
+	if (voltage < 3.6)
+		speaker_warn_low_battery();
+	if (voltage < 3.5)
+		speaker_warn_low_battery();
+	if (voltage < 3.4)
+		speaker_warn_low_battery();
+	if (voltage < 3.3)
+		speaker_play_error();
+}
+
 /**
  * @brief Includes the functions to be executed before robot starts to move.
  */
@@ -55,6 +74,7 @@ static void before_moving(void)
 	disable_walls_control();
 	repeat_blink(10, 100);
 	sleep_us(5000000);
+	check_battery_voltage();
 	led_left_on();
 	led_right_on();
 	wait_front_sensor_close_signal(0.12);
@@ -75,9 +95,11 @@ static void after_moving(void)
 		reset_motion();
 		blink_collision();
 	} else {
+		speaker_play_success();
 		repeat_blink(10, 100);
 	}
 	reset_motion();
+	check_battery_voltage();
 }
 
 /**
diff --git a/src/setup.c b/src/setup.c
index 540d89bd..70ed2942 100644
--- a/src/setup.c
+++ b/src/setup.c
@@ -218,7 +218,7 @@ void setup_spi_low_speed(void)
  * @see Reference manual (RM0008) "TIMx functional description" and in
  * particular "PWM mode" section.
  */
-static void setup_pwm(void)
+static void setup_motor_driver(void)
 {
 	timer_set_mode(TIM3, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE,
 		       TIM_CR1_DIR_UP);
@@ -252,6 +252,48 @@ static void setup_pwm(void)
 	timer_enable_counter(TIM3);
 }
 
+/**
+ * @brief Setup PWM for the speaker.
+ *
+ * TIM1 is used to generate the PWM signals for the speaker:
+ *
+ * - Configure channel 3 as output GPIO.
+ * - Edge-aligned, up-counting timer.
+ * - Prescale to increment timer counter at TIM1CLK_FREQUENCY_HZ.
+ * - Set output compare mode to PWM1 (output is active when the counter is
+ *   less than the compare register contents and inactive otherwise.
+ * - Disable output compare output (speaker is off by default).
+ * - Enable outputs in the break subsystem.
+ *
+ * @see Reference manual (RM0008) "TIMx functional description" and in
+ * particular "PWM mode" section.
+ */
+void setup_speaker(void)
+{
+	rcc_periph_reset_pulse(RST_TIM1);
+
+	gpio_set_mode(GPIOA, GPIO_MODE_OUTPUT_50_MHZ,
+		      GPIO_CNF_OUTPUT_ALTFN_PUSHPULL, GPIO_TIM1_CH3);
+
+	/* Make sure to turn emitters off */
+	gpio_clear(GPIOA, GPIO8 | GPIO9);
+	gpio_clear(GPIOB, GPIO8 | GPIO9);
+
+	timer_set_mode(TIM1, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE,
+		       TIM_CR1_DIR_UP);
+
+	timer_set_prescaler(
+	    TIM1, (rcc_apb2_frequency / SPEAKER_BASE_FREQUENCY_HZ - 1));
+	timer_set_repetition_counter(TIM1, 0);
+	timer_enable_preload(TIM1);
+	timer_continuous_mode(TIM1);
+
+	timer_disable_oc_output(TIM1, TIM_OC3);
+	timer_set_oc_mode(TIM1, TIM_OC3, TIM_OCM_PWM1);
+
+	timer_enable_break_main_output(TIM1);
+}
+
 /**
  * @brief Configure timer to read a quadrature encoder.
  *
@@ -428,9 +470,10 @@ static void setup_adc2(void)
  *
  * @see Reference manual (RM0008) "Advanced-control timers"
  */
-static void setup_timer1(void)
+void setup_emitters(void)
 {
 	rcc_periph_reset_pulse(RST_TIM1);
+
 	timer_set_mode(TIM1, TIM_CR1_CKD_CK_INT, TIM_CR1_CMS_EDGE,
 		       TIM_CR1_DIR_UP);
 	timer_set_clock_division(TIM1, 0x00);
@@ -452,9 +495,9 @@ void setup(void)
 	setup_adc2();
 	setup_usart();
 	setup_encoders();
-	setup_pwm();
+	setup_motor_driver();
 	setup_mpu();
 	setup_systick();
-	setup_timer1();
+	setup_emitters();
 	setup_adc1();
 }
diff --git a/src/setup.h b/src/setup.h
index 8da9b7ea..ee18907f 100644
--- a/src/setup.h
+++ b/src/setup.h
@@ -26,6 +26,7 @@
 
 /** System clock frequency is set in `setup_clock` */
 #define SYSCLK_FREQUENCY_HZ 72000000
+#define SPEAKER_BASE_FREQUENCY_HZ 1000000
 #define SYSTICK_FREQUENCY_HZ 1000
 #define DRIVER_PWM_PERIOD 1024
 
@@ -59,6 +60,8 @@
 #define BATTERY_LOW_LIMIT_VOLTAGE 3.3
 
 void setup(void);
+void setup_emitters(void);
+void setup_speaker(void);
 void setup_spi_low_speed(void);
 void setup_spi_high_speed(void);
 void enable_systick_interruption(void);
diff --git a/src/speaker.c b/src/speaker.c
new file mode 100644
index 00000000..3ad10ee4
--- /dev/null
+++ b/src/speaker.c
@@ -0,0 +1,81 @@
+#include "speaker.h"
+
+/**
+ * Number of semitones above C, for each note in an octave.
+ *
+ * Notes are in order: {A, B, C, D, E, F, G}.
+ */
+uint8_t SEMITONES[8] = {9, 11, 0, 2, 4, 5, 7};
+
+/**
+ * Base or reference note, used for the pitch.
+ */
+uint8_t BASE_NOTE = 9;
+uint8_t BASE_OCTAVE = 4;
+float BASE_FREQUENCY = 440.;
+
+/**
+ * @brief Set the frequency for the speaker.
+ *
+ * Frequency is set modulating the PWM signal sent to the speaker.
+ *
+ * @param[in] hz Frequency, in Hertz.
+ */
+static void speaker_set_frequency(float hz)
+{
+	uint16_t period;
+
+	period = (uint16_t)(SPEAKER_BASE_FREQUENCY_HZ / hz);
+	timer_set_period(TIM1, period);
+	timer_set_oc_value(TIM1, TIM_OC3, period / 2);
+}
+
+/**
+ * @brief Turn on the speaker to play the set frequency.
+ */
+static void speaker_on(void)
+{
+	timer_enable_counter(TIM1);
+	timer_enable_oc_output(TIM1, TIM_OC3);
+}
+
+/**
+ * @brief Turn off the speaker.
+ */
+static void speaker_off(void)
+{
+	timer_disable_counter(TIM1);
+	timer_disable_oc_output(TIM1, TIM_OC3);
+}
+
+/**
+ * @brief Play a note through the speaker.
+ *
+ * Even if this function uses the scientific notation, notes are played with
+ * the concert pitch (standard pitch). That means A above middle C is the
+ * reference note, played at 440 Hz.
+ *
+ * @param[in] note Which note to play, in scientific notation.
+ * @param[in] octave Which octave to play, in scientific notation.
+ * @param[in] accidental Number of semitones to sum to the note.
+ * @param[in] duration Duration of the note, in seconds.
+ *
+ * @note The speaker and emitters both share TIM1. While playing a note, the
+ * emitters will be completely disabled and enabled back only after finishing
+ * playing the note.
+ */
+void speaker_play(char note, uint8_t octave, int8_t accidental, float duration)
+{
+	int16_t sound;
+	float frequency;
+
+	sound = SEMITONES[note - 'A'] - BASE_NOTE + (octave - BASE_OCTAVE) * 12;
+	sound += accidental;
+	frequency = pow(2, sound / 12.) * BASE_FREQUENCY;
+	setup_speaker();
+	speaker_set_frequency(frequency);
+	speaker_on();
+	sleep_seconds(duration);
+	speaker_off();
+	setup_emitters();
+}
diff --git a/src/speaker.h b/src/speaker.h
new file mode 100644
index 00000000..39b90066
--- /dev/null
+++ b/src/speaker.h
@@ -0,0 +1,12 @@
+#ifndef __SPEAKER_H
+#define __SPEAKER_H
+
+#include <math.h>
+
+#include <libopencm3/stm32/timer.h>
+
+#include "setup.h"
+
+void speaker_play(char note, uint8_t octave, int8_t accidental, float duration);
+
+#endif /* __SPEAKER_H */