diff --git a/src/components/store-consumer/store-consumer.tsx b/src/components/store-consumer/store-consumer.tsx
index 101be03..30fe250 100644
--- a/src/components/store-consumer/store-consumer.tsx
+++ b/src/components/store-consumer/store-consumer.tsx
@@ -3,6 +3,7 @@ import { useEffect } from 'react';
 import { useSoundStore } from '@/stores/sound';
 import { useNoteStore } from '@/stores/note';
 import { usePresetStore } from '@/stores/preset';
+import { useCountdownTimers } from '@/stores/countdown-timers';
 
 interface StoreConsumerProps {
   children: React.ReactNode;
@@ -13,6 +14,7 @@ export function StoreConsumer({ children }: StoreConsumerProps) {
     useSoundStore.persist.rehydrate();
     useNoteStore.persist.rehydrate();
     usePresetStore.persist.rehydrate();
+    useCountdownTimers.persist.rehydrate();
   }, []);
 
   return <>{children}</>;
diff --git a/src/components/toolbox/countdown-timer/countdown-timer.tsx b/src/components/toolbox/countdown-timer/countdown-timer.tsx
index 378066d..3be8a4b 100644
--- a/src/components/toolbox/countdown-timer/countdown-timer.tsx
+++ b/src/components/toolbox/countdown-timer/countdown-timer.tsx
@@ -1,6 +1,7 @@
 import { Modal } from '@/components/modal';
 
 import { Form } from './form';
+import { Timers } from './timers';
 
 interface TimerProps {
   onClose: () => void;
@@ -10,8 +11,8 @@ interface TimerProps {
 export function CountdownTimer({ onClose, show }: TimerProps) {
   return (
     <Modal show={show} onClose={onClose}>
-      <h1>Hello World</h1>
       <Form />
+      <Timers />
     </Modal>
   );
 }
diff --git a/src/components/toolbox/countdown-timer/timers/index.ts b/src/components/toolbox/countdown-timer/timers/index.ts
new file mode 100644
index 0000000..0f9e27a
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/index.ts
@@ -0,0 +1 @@
+export { Timers } from './timers';
diff --git a/src/components/toolbox/countdown-timer/timers/notice/index.ts b/src/components/toolbox/countdown-timer/timers/notice/index.ts
new file mode 100644
index 0000000..64af78d
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/notice/index.ts
@@ -0,0 +1 @@
+export { Notice } from './notice';
diff --git a/src/components/toolbox/countdown-timer/timers/notice/notice.module.css b/src/components/toolbox/countdown-timer/timers/notice/notice.module.css
new file mode 100644
index 0000000..54c58c0
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/notice/notice.module.css
@@ -0,0 +1,10 @@
+.notice {
+  padding: 16px;
+  margin-top: 16px;
+  font-size: var(--font-sm);
+  line-height: 1.65;
+  color: var(--color-foreground-subtle);
+  text-align: center;
+  border: 1px dashed var(--color-neutral-200);
+  border-radius: 8px;
+}
diff --git a/src/components/toolbox/countdown-timer/timers/notice/notice.tsx b/src/components/toolbox/countdown-timer/timers/notice/notice.tsx
new file mode 100644
index 0000000..a25b74c
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/notice/notice.tsx
@@ -0,0 +1,10 @@
+import styles from './notice.module.css';
+
+export function Notice() {
+  return (
+    <p className={styles.notice}>
+      Please do not close this tab while timers are running, otherwise all
+      timers will be stopped.
+    </p>
+  );
+}
diff --git a/src/components/toolbox/countdown-timer/timers/timer/index.ts b/src/components/toolbox/countdown-timer/timers/timer/index.ts
new file mode 100644
index 0000000..91b3f08
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timer/index.ts
@@ -0,0 +1 @@
+export { Timer } from './timer';
diff --git a/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/index.ts b/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/index.ts
new file mode 100644
index 0000000..03e8ec4
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/index.ts
@@ -0,0 +1 @@
+export { ReverseTimer } from './reverse-timer';
diff --git a/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/reverse-timer.module.css b/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/reverse-timer.module.css
new file mode 100644
index 0000000..ca62729
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/reverse-timer.module.css
@@ -0,0 +1,9 @@
+.reverseTimer {
+  position: absolute;
+  top: 15px;
+  left: 50%;
+  font-size: var(--font-xsm);
+  color: var(--color-foreground-subtle);
+  letter-spacing: 1px;
+  transform: translate(-50%);
+}
diff --git a/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/reverse-timer.tsx b/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/reverse-timer.tsx
new file mode 100644
index 0000000..5a10532
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timer/reverse-timer/reverse-timer.tsx
@@ -0,0 +1,21 @@
+import { useMemo } from 'react';
+
+import { padNumber } from '@/helpers/number';
+
+import styles from './reverse-timer.module.css';
+
+interface ReverseTimerProps {
+  spent: number;
+}
+
+export function ReverseTimer({ spent }: ReverseTimerProps) {
+  const hours = useMemo(() => Math.floor(spent / 3600), [spent]);
+  const minutes = useMemo(() => Math.floor((spent % 3600) / 60), [spent]);
+  const seconds = useMemo(() => spent % 60, [spent]);
+
+  return (
+    <div className={styles.reverseTimer}>
+      -{padNumber(hours)}:{padNumber(minutes)}:{padNumber(seconds)}
+    </div>
+  );
+}
diff --git a/src/components/toolbox/countdown-timer/timers/timer/timer.module.css b/src/components/toolbox/countdown-timer/timers/timer/timer.module.css
new file mode 100644
index 0000000..dbcad09
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timer/timer.module.css
@@ -0,0 +1,125 @@
+.timer {
+  position: relative;
+  padding: 8px;
+  overflow: hidden;
+  background-color: var(--color-neutral-100);
+  border: 1px solid var(--color-neutral-200);
+  border-radius: 8px;
+
+  &:not(:last-of-type) {
+    margin-bottom: 24px;
+  }
+
+  & .header {
+    position: relative;
+    top: -8px;
+    width: 100%;
+
+    & .bar {
+      height: 2px;
+      margin: 0 -8px;
+      background-color: var(--color-neutral-200);
+
+      & .completed {
+        height: 100%;
+        background-color: var(--color-neutral-500);
+        transition: 0.2s;
+      }
+    }
+  }
+
+  & .footer {
+    display: flex;
+    column-gap: 4px;
+    align-items: center;
+
+    & .control {
+      display: flex;
+      flex-grow: 1;
+      column-gap: 4px;
+      align-items: center;
+      height: 40px;
+      padding: 4px;
+      background-color: var(--color-neutral-50);
+      border: 1px solid var(--color-neutral-200);
+      border-radius: 4px;
+
+      & .input {
+        flex-grow: 1;
+        width: 100%;
+        min-width: 0;
+        height: 100%;
+        padding: 0 8px;
+        color: var(--color-foreground-subtle);
+        background-color: transparent;
+        border: none;
+        border-radius: 4px;
+        outline: none;
+
+        &.finished {
+          text-decoration: line-through;
+        }
+      }
+
+      & .button {
+        display: flex;
+        align-items: center;
+        justify-content: center;
+        height: 100%;
+        aspect-ratio: 1 / 1;
+        color: var(--color-foreground);
+        cursor: pointer;
+        background-color: var(--color-neutral-200);
+        border: 1px solid var(--color-neutral-300);
+        border-radius: 2px;
+        outline: none;
+        transition: 0.2s;
+
+        &.reset {
+          background-color: var(--color-neutral-100);
+          border: none;
+        }
+
+        &:disabled,
+        &.disabled {
+          cursor: not-allowed;
+          opacity: 0.6;
+        }
+      }
+    }
+
+    & .delete {
+      display: flex;
+      align-items: center;
+      justify-content: center;
+      width: 38px;
+      height: 38px;
+      color: #f43f5e;
+      cursor: pointer;
+      background-color: rgb(244 63 94 / 10%);
+      border: none;
+      border-radius: 4px;
+      outline: none;
+      transition: 0.2s;
+
+      &.disabled {
+        cursor: not-allowed;
+        opacity: 0.6;
+      }
+    }
+  }
+
+  & .left {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    height: 120px;
+    font-family: var(--font-mono);
+    font-size: var(--font-2xlg);
+    font-weight: 700;
+
+    & span {
+      color: var(--color-foreground-subtle);
+    }
+  }
+}
diff --git a/src/components/toolbox/countdown-timer/timers/timer/timer.tsx b/src/components/toolbox/countdown-timer/timers/timer/timer.tsx
new file mode 100644
index 0000000..7bd7107
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timer/timer.tsx
@@ -0,0 +1,188 @@
+import { useRef, useMemo, useState, useEffect } from 'react';
+import { IoPlay, IoPause, IoRefresh, IoTrashOutline } from 'react-icons/io5';
+
+import { ReverseTimer } from './reverse-timer';
+
+import { useCountdownTimers } from '@/stores/countdown-timers';
+import { useAlarm } from '@/hooks/use-alarm';
+import { useSnackbar } from '@/contexts/snackbar';
+import { padNumber } from '@/helpers/number';
+import { cn } from '@/helpers/styles';
+
+import styles from './timer.module.css';
+
+interface TimerProps {
+  id: string;
+}
+
+export function Timer({ id }: TimerProps) {
+  const intervalRef = useRef<ReturnType<typeof setInterval> | null>(null);
+  const lastActiveTimeRef = useRef<number | null>(null);
+  const lastStateRef = useRef<{ spent: number; total: number } | null>(null);
+
+  const [isRunning, setIsRunning] = useState(false);
+
+  const { name, spent, total } = useCountdownTimers(state =>
+    state.getTimer(id),
+  );
+  const tick = useCountdownTimers(state => state.tick);
+  const rename = useCountdownTimers(state => state.rename);
+  const reset = useCountdownTimers(state => state.reset);
+  const deleteTimer = useCountdownTimers(state => state.delete);
+
+  const left = useMemo(() => total - spent, [total, spent]);
+
+  const hours = useMemo(() => Math.floor(left / 3600), [left]);
+  const minutes = useMemo(() => Math.floor((left % 3600) / 60), [left]);
+  const seconds = useMemo(() => left % 60, [left]);
+
+  const playAlarm = useAlarm();
+
+  const showSnackbar = useSnackbar();
+
+  const handleStart = () => {
+    if (left > 0) setIsRunning(true);
+  };
+
+  const handlePause = () => setIsRunning(false);
+
+  const handleToggle = () => {
+    if (isRunning) handlePause();
+    else handleStart();
+  };
+
+  const handleReset = () => {
+    if (spent === 0) return;
+
+    if (isRunning) return showSnackbar('Please first stop the timer.');
+
+    setIsRunning(false);
+    reset(id);
+  };
+
+  const handleDelete = () => {
+    if (isRunning) return showSnackbar('Please first stop the timer.');
+
+    deleteTimer(id);
+  };
+
+  useEffect(() => {
+    if (isRunning) {
+      if (intervalRef.current) clearInterval(intervalRef.current);
+
+      intervalRef.current = setInterval(() => tick(id), 1000);
+    }
+
+    return () => {
+      if (intervalRef.current) clearInterval(intervalRef.current);
+    };
+  }, [isRunning, tick, id]);
+
+  useEffect(() => {
+    if (left === 0 && isRunning) {
+      setIsRunning(false);
+      playAlarm();
+
+      if (intervalRef.current) clearInterval(intervalRef.current);
+    }
+  }, [left, isRunning, playAlarm]);
+
+  useEffect(() => {
+    const handleBlur = () => {
+      if (isRunning) {
+        lastActiveTimeRef.current = Date.now();
+        lastStateRef.current = { spent, total };
+      }
+    };
+
+    const handleFocus = () => {
+      if (isRunning && lastActiveTimeRef.current && lastStateRef.current) {
+        const elapsed = Math.floor(
+          (Date.now() - lastActiveTimeRef.current) / 1000,
+        );
+        const previousLeft =
+          lastStateRef.current.total - lastStateRef.current.spent;
+        const currentLeft = left;
+        const correctedLeft = previousLeft - elapsed;
+
+        if (correctedLeft < currentLeft) {
+          tick(id, currentLeft - correctedLeft);
+        }
+
+        lastActiveTimeRef.current = null;
+        lastStateRef.current = null;
+      }
+    };
+
+    window.addEventListener('blur', handleBlur);
+    window.addEventListener('focus', handleFocus);
+
+    return () => {
+      window.removeEventListener('blur', handleBlur);
+      window.removeEventListener('focus', handleFocus);
+    };
+  }, [isRunning, tick, id, spent, total, left]);
+
+  return (
+    <div className={styles.timer}>
+      <header className={styles.header}>
+        <div className={styles.bar}>
+          <div
+            className={styles.completed}
+            style={{ width: `${(left / total) * 100}%` }}
+          />
+        </div>
+      </header>
+
+      <ReverseTimer spent={spent} />
+
+      <div className={styles.left}>
+        {padNumber(hours)}
+        <span>:</span>
+        {padNumber(minutes)}
+        <span>:</span>
+        {padNumber(seconds)}
+      </div>
+
+      <footer className={styles.footer}>
+        <div className={styles.control}>
+          <input
+            className={cn(styles.input, left === 0 && styles.finished)}
+            placeholder="Untitled"
+            type="text"
+            value={name}
+            onChange={e => rename(id, e.target.value)}
+          />
+
+          <button
+            aria-disabled={isRunning || spent === 0}
+            className={cn(
+              styles.button,
+              styles.reset,
+              (isRunning || spent === 0) && styles.disabled,
+            )}
+            onClick={handleReset}
+          >
+            <IoRefresh />
+          </button>
+
+          <button
+            className={styles.button}
+            disabled={!isRunning && left === 0}
+            onClick={handleToggle}
+          >
+            {isRunning ? <IoPause /> : <IoPlay />}
+          </button>
+        </div>
+
+        <button
+          aria-disabled={isRunning}
+          className={cn(styles.delete, isRunning && styles.disabled)}
+          onClick={handleDelete}
+        >
+          <IoTrashOutline />
+        </button>
+      </footer>
+    </div>
+  );
+}
diff --git a/src/components/toolbox/countdown-timer/timers/timers.module.css b/src/components/toolbox/countdown-timer/timers/timers.module.css
new file mode 100644
index 0000000..e8cc2c6
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timers.module.css
@@ -0,0 +1,27 @@
+.timers {
+  margin-top: 48px;
+
+  & > header {
+    display: flex;
+    column-gap: 12px;
+    align-items: center;
+    margin-bottom: 16px;
+
+    & .title {
+      font-family: var(--font-display);
+      font-size: var(--font-lg);
+      line-height: 1;
+    }
+
+    & .line {
+      flex-grow: 1;
+      height: 0;
+      border-top: 1px dashed var(--color-neutral-200);
+    }
+
+    & .spent {
+      font-size: var(--font-sm);
+      color: var(--color-foreground-subtle);
+    }
+  }
+}
diff --git a/src/components/toolbox/countdown-timer/timers/timers.tsx b/src/components/toolbox/countdown-timer/timers/timers.tsx
new file mode 100644
index 0000000..daa35b7
--- /dev/null
+++ b/src/components/toolbox/countdown-timer/timers/timers.tsx
@@ -0,0 +1,42 @@
+import { useMemo } from 'react';
+
+import { Timer } from './timer';
+import { Notice } from './notice';
+
+import { useCountdownTimers } from '@/stores/countdown-timers';
+
+import styles from './timers.module.css';
+
+export function Timers() {
+  const timers = useCountdownTimers(state => state.timers);
+  const spent = useCountdownTimers(state => state.spent());
+  const total = useCountdownTimers(state => state.total());
+
+  const spentMinutes = useMemo(() => Math.floor(spent / 60), [spent]);
+  const totalMinutes = useMemo(() => Math.floor(total / 60), [total]);
+
+  return (
+    <div>
+      {timers.length > 0 ? (
+        <div className={styles.timers}>
+          <header>
+            <h2 className={styles.title}>Timers</h2>
+            <div className={styles.line} />
+            {totalMinutes > 0 && (
+              <p className={styles.spent}>
+                {spentMinutes} / {totalMinutes} Minute
+                {totalMinutes !== 1 && 's'}
+              </p>
+            )}
+          </header>
+
+          {timers.map(timer => (
+            <Timer id={timer.id} key={timer.id} />
+          ))}
+
+          <Notice />
+        </div>
+      ) : null}
+    </div>
+  );
+}
diff --git a/src/hooks/use-alarm.ts b/src/hooks/use-alarm.ts
new file mode 100644
index 0000000..b2c8f35
--- /dev/null
+++ b/src/hooks/use-alarm.ts
@@ -0,0 +1,24 @@
+import { useCallback } from 'react';
+
+import { useSound } from './use-sound';
+import { useAlarmStore } from '@/stores/alarm';
+
+export function useAlarm() {
+  const { play: playSound } = useSound(
+    '/sounds/alarm.mp3',
+    { volume: 1 },
+    true,
+  );
+  const isPlaying = useAlarmStore(state => state.isPlaying);
+  const play = useAlarmStore(state => state.play);
+  const stop = useAlarmStore(state => state.stop);
+
+  const playAlarm = useCallback(() => {
+    if (!isPlaying) {
+      playSound(stop);
+      play();
+    }
+  }, [isPlaying, playSound, play, stop]);
+
+  return playAlarm;
+}
diff --git a/src/hooks/use-sound.ts b/src/hooks/use-sound.ts
index 88fab70..934092d 100644
--- a/src/hooks/use-sound.ts
+++ b/src/hooks/use-sound.ts
@@ -26,7 +26,8 @@ import { FADE_OUT } from '@/constants/events';
  */
 export function useSound(
   src: string,
-  options: { loop?: boolean; volume?: number } = {},
+  options: { loop?: boolean; preload?: boolean; volume?: number } = {},
+  html5: boolean = false,
 ) {
   const [hasLoaded, setHasLoaded] = useState(false);
   const isLoading = useLoadingStore(state => state.loaders[src]);
@@ -38,17 +39,18 @@ export function useSound(
 
     if (isBrowser) {
       sound = new Howl({
+        html5,
         onload: () => {
           setIsLoading(src, false);
           setHasLoaded(true);
         },
-        preload: false,
+        preload: options.preload ?? false,
         src: src,
       });
     }
 
     return sound;
-  }, [src, isBrowser, setIsLoading]);
+  }, [src, isBrowser, setIsLoading, html5, options.preload]);
 
   useEffect(() => {
     if (sound) {
@@ -60,18 +62,23 @@ export function useSound(
     if (sound) sound.volume(options.volume ?? 0.5);
   }, [sound, options.volume]);
 
-  const play = useCallback(() => {
-    if (sound) {
-      if (!hasLoaded && !isLoading) {
-        setIsLoading(src, true);
-        sound.load();
-      }
+  const play = useCallback(
+    (cb?: () => void) => {
+      if (sound) {
+        if (!hasLoaded && !isLoading) {
+          setIsLoading(src, true);
+          sound.load();
+        }
 
-      if (!sound.playing()) {
-        sound.play();
+        if (!sound.playing()) {
+          sound.play();
+        }
+
+        if (typeof cb === 'function') sound.once('end', cb);
       }
-    }
-  }, [src, setIsLoading, sound, hasLoaded, isLoading]);
+    },
+    [src, setIsLoading, sound, hasLoaded, isLoading],
+  );
 
   const stop = useCallback(() => {
     if (sound) sound.stop();
diff --git a/src/stores/alarm/index.ts b/src/stores/alarm/index.ts
new file mode 100644
index 0000000..2c981d1
--- /dev/null
+++ b/src/stores/alarm/index.ts
@@ -0,0 +1,19 @@
+import { create } from 'zustand';
+
+interface AlarmStore {
+  isPlaying: boolean;
+  play: () => void;
+  stop: () => void;
+}
+
+export const useAlarmStore = create<AlarmStore>()(set => ({
+  isPlaying: false,
+
+  play() {
+    set({ isPlaying: true });
+  },
+
+  stop() {
+    set({ isPlaying: false });
+  },
+}));