diff --git a/src/lib/Firebase/messages.js b/src/lib/Firebase/messages.js
index b216022..d834fb8 100644
--- a/src/lib/Firebase/messages.js
+++ b/src/lib/Firebase/messages.js
@@ -1,6 +1,8 @@
-import { collection, query, where, getDocs } from 'firebase/firestore'; // tools for building and running db queries
+import { collection, query, where, getDocs, addDoc } from 'firebase/firestore'; // tools for building and running db queries
 import { db } from './config'; // database connection
 import { getQueryPrefix } from '$lib/utils/geohash'; // convert coordinates into geohash string 
+import { doc, updateDoc, increment, serverTimestamp } from 'firebase/firestore';
+import ngeohash from 'ngeohash';
 
 export async function getNearbyMessages(lat, lng) {
     const prefix = getQueryPrefix(lat, lng);
@@ -13,4 +15,37 @@ export async function getNearbyMessages(lat, lng) {
 
     const snapshot = await getDocs(q);
     return snapshot.docs.map(doc => ({ id: doc.id, ...doc.data() }));
+}
+
+export async function echoMessage(messageId) {
+    const ref = doc(db, 'messages', messageId);
+    await updateDoc(ref, {
+        echoCount: increment(1),
+        lastEchoAt: serverTimestamp()
+    });
+}
+
+export async function addMessage(lat, lng, text, imageUrl = ''){
+    const geohash = ngeohash.encode(lat, lng, 6);
+
+    await addDoc(collection(db, 'messages'), {
+        text, 
+        imageUrl, 
+        lat, 
+        lng,
+        geohash, 
+        createdAt: serverTimestamp(),
+        lastEchoAt: serverTimestamp(),
+        echoCount: 0,
+        sessionId: getSessionId()
+    });
+}
+
+function getSessionId() {
+    let id = localStorage.getItem('overheard_session');
+    if (!id) {
+        id = crypto.randomUUID(); // created random useer id 
+        localStorage.setItem('oveheard_session', id);
+    }
+    return id;
 }
\ No newline at end of file
diff --git a/src/lib/components/BottomSheet.svelte b/src/lib/components/BottomSheet.svelte
index df45f62..9b4e001 100644
--- a/src/lib/components/BottomSheet.svelte
+++ b/src/lib/components/BottomSheet.svelte
@@ -1,7 +1,20 @@
 <script>
     import { mapStore } from '$lib/stores/mapStore.js';
+    import { getDecayInfo } from '$lib/utils/time.js'
+    import { echoMessage } from '$lib/firebase/messages.js'
 
     let { message } = $props();
+
+    let decay = $derived(
+        message ? getDecayInfo(message.createdAt, message.lastEchoAt) : null
+    );
+
+    let echoed = $state(false);
+
+    async function handleEcho() {
+        await echoMessage(message.id);
+        echoed = true;
+    }
 </script>
 
 <!-- if message exists, sheet is visible -->
@@ -10,11 +23,16 @@
         <div class="handle">    </div>
         <div class="content">
             <p class="message-text">{message.text}</p>
-            <p class="meta">
-                left {message.lat.toFixed(4)}, {message.lng.toFixed(4)}
-            </p>
+            {#if decay}
+                <p class="meta">left {decay.daysAgo} days ago. fading in {decay.daysLeft} days.</p>
+            {/if}
             <div class="actions">
-                <button class="echo-button">Echo</button>
+                <button class="echo-button" 
+                class:echoed={echoed} 
+                onclick={handleEcho} 
+                disabled={echoed}>
+                    {echoed ? 'Echoed' : 'Echo'}
+                </button>
                 <button class="letgo-button" onclick={() => mapStore.set(
                     { selectedMessage: null, composing: false })}>
                     let go
@@ -90,5 +108,14 @@
         font-size: 0.95rem;
         cursor: pointer;
     }
-    
+
+    .echo-button.echoed {
+        background: #4ecdc4;
+        animation: pulsate 1.5s ease-in-out 3;
+    }
+
+    @keyframes pulsate {
+        0%, 100% {box-shadow: 0 0 0 0 rgba(78,205,196,0.4); }
+        50% {box-shadow: 0 0 0 12px rgba(78, 205, 196, 0);}
+    }
 </style>
\ No newline at end of file
diff --git a/src/lib/components/ComposeSheet.svelte b/src/lib/components/ComposeSheet.svelte
new file mode 100644
index 0000000..50c662b
--- /dev/null
+++ b/src/lib/components/ComposeSheet.svelte
@@ -0,0 +1,138 @@
+<script>
+    import { mapStore } from '$lib/stores/mapStore.js';
+    import { messagesStore } from '$lib/stores/messagesStore.js';
+    import { addMessage } from '$lib/firebase/messages.js'
+
+    let {lat, lng} = $props();
+
+    let text = $state('');
+    let submitting = $state(false);
+    let remaining = $derived(240-text.length);
+
+    async function handleSubmit() {
+        if (!text.trim() || remaining < 0) return;
+        submitting = true;
+
+        await addMessage(lat, lng, text.trim());
+
+        //refresh the messages store so pin is there
+        const { getNearbyMessages } = await import('$lib/firebase/messages.js');
+        const updated = await getNearbyMessages(lat, lng);
+        messagesStore.set(updated);
+
+        //reset and close
+        text = '';
+        submitting = false;
+        mapStore.set({selectedMessage: null, composing: false});
+    }
+
+</script>
+
+<div class="compose" class:visible={true}>
+    <div class="compose-header">
+        <button class="cancel" onclick={() => mapStore.set(
+            {selectedMessage: null, composing: false}
+        )}> 
+        Cancel
+        </button>
+        <span class="title">Leave a message</span> 
+        <span class="counter" class:over={remaining < 0}>{remaining}</span>
+    </div>
+
+    <textarea
+        bind:value={text}
+        placeholder="Share a moment for someone else to overhear"
+        rows="5"
+    ></textarea>
+
+    <button 
+    class="submit"
+    onclick={handleSubmit}
+    disabled={!text.trim() || remaining < 0 || submitting}>
+        {submitting ? "leaving it here..." : "leave it here"}    
+    </button>
+
+</div>
+
+<style>
+    .compose {
+        position: fixed;
+        bottom: 0;
+        left: 0;
+        right: 0;
+        background: white;
+        border-radius: 20px 20px 0 0;
+        padding: 1.2rem 1.5rem 2.5rem;
+        box-shadow: 0 -4px 20px rgba(0,0,0,0.15);
+        z-index: 200;
+    }
+
+    .compose-header {
+        display: flex;
+        align-items: center;
+        justify-content: space-between;
+        margin-bottom: 1rem;
+    }
+
+    .title {
+        font-weight: 600;
+        font-size: 0.95rem;
+        color: #111;
+    }
+
+    .cancel {
+        background: none;
+        border: none;
+        color: #999;
+        font-size: 0.9rem;
+        cursor: pointer;
+        padding: 0;
+    }
+
+    .counter {
+        font-size: 0.85rem;
+        color: #999;
+        font-variant-numeric: tublar-nums; 
+    }
+
+    .counter.over {
+        color: #e74c3c;
+        font-weight: 600;
+    }
+
+    textarea {
+        width: 100%;
+        border: 1.5px solid #eee;
+        border-radius: 12px;
+        padding: 0.9rem;
+        font-size: 0.95rem;
+        line-height: 1.6;
+        resize: none;
+        outline: none;
+        font-family: Georgia, 'Times New Roman', Times, serif;
+        color: #111;
+    }
+
+    textarea:focus {
+        border-color: #111;
+    }
+
+    .submit {
+        width: 100%;
+        margin-top: 0.75rem;
+        padding: 0.85rem;
+        background: #111;
+        color: white;
+        border: none;
+        border-radius: 12px;
+        font-size: 0.95rem;
+        font-weight: 500;
+        cursor: pointer;
+    }
+
+    .submit:disabled {
+        background: #ccc;
+        cursor: not-allowed;
+    }
+</style>
+
diff --git a/src/lib/components/SidePanel.svelte b/src/lib/components/SidePanel.svelte
index e432286..324655d 100644
--- a/src/lib/components/SidePanel.svelte
+++ b/src/lib/components/SidePanel.svelte
@@ -1,18 +1,36 @@
 <script>
     import { mapStore } from '$lib/stores/mapStore.js';
+    import { getDecayInfo } from '$lib/utils/time.js';
+    import { echoMessage } from '$lib/firebase/messages.js'
 
     let { message } = $props(); 
+
+    let decay = $derived(
+        message ? getDecayInfo(message.createdAt, message.lastEchoAt) : null
+    );
+
+    let echoed = $state(false);
+
+    async function handleEcho() {
+        await echoMessage(message.id);
+        echoed = true;
+    }
 </script>
 
 <div class = "panel">
     {#if message}
         <div class="content">
             <p class="message-text">{message.text}</p>
-            <p class="meta">
-                left {message.lat.toFixed(4)}, {message.lng.toFixed(4)}
-            </p>
+            {#if decay}
+                <p class="meta">left {decay.daysAgo} days ago. fading in {decay.daysLeft} days.</p>
+            {/if}
             <div class="actions">
-                <button class="echo-button">Echo</button>
+                <button class="echo-button" 
+                class:echoed={echoed} 
+                onclick={handleEcho} 
+                disabled={echoed}>
+                    {echoed ? 'Echoed' : 'Echo'}
+                </button>
                 <button class="letgo-button" onclick={() => mapStore.set(
                     {selectedMessage: null, composing: false})}>
                     Let go
@@ -87,6 +105,15 @@
         margin-top: 2rem;
         text-align: center;
     }
-    
+
+    .echo-button.echoed {
+        background: #4ecdc4;
+        animation: pulsate 1.5s ease-in-out 3;
+    }
+
+    @keyframes pulsate {
+        0%, 100% {box-shadow: 0 0 0 0 rgba(78,205,196,0.4); }
+        50% {box-shadow: 0 0 0 12px rgba(78, 205, 196, 0);}
+    }
 </style>
 
diff --git a/src/lib/utils/time.js b/src/lib/utils/time.js
new file mode 100644
index 0000000..bc683f9
--- /dev/null
+++ b/src/lib/utils/time.js
@@ -0,0 +1,15 @@
+export function getDecayInfo(createdAt, lastEchoAt) {
+    const now = Date.now();
+    const echoTime = lastEchoAt?.toMillis() ?? createdAt.toMillis();
+    const createdTime = createdAt.toMillis(); 
+
+    const daysSinceCreated = Math.floor((now - createdTime) / (1000 * 60 * 60 * 24));
+    const daysSinceEcho = Math.floor((now - echoTime)/(1000 * 60 * 60 * 24));
+    const daysLeft = 30 - daysSinceEcho;
+
+    return {
+        daysAgo: daysSinceCreated,
+        daysLeft: Math.max(0, daysLeft),
+        isExpired: daysLeft <= 0
+    };
+}
\ No newline at end of file
diff --git a/src/routes/+page.svelte b/src/routes/+page.svelte
index 9635369..df4c21b 100644
--- a/src/routes/+page.svelte
+++ b/src/routes/+page.svelte
@@ -9,6 +9,8 @@
     import BottomSheet from '$lib/components/BottomSheet.svelte';
     import SidePanel from '$lib/components/SidePanel.svelte';
 
+    import ComposeSheet from '$lib/components/ComposeSheet.svelte';
+
     let lat = $state();
     let lng = $state();
     let error = $state();
@@ -66,6 +68,22 @@
     <SidePanel message={$mapStore.selectedMessage} />
 {/if}
 
+<!--floating action button for adding a message-->
+{#if !$mapStore.composing}
+    <button
+    class="fab"
+    onclick={() => mapStore.set(
+        {selectedMessage: null, composing: true })}>
+    +
+    </button>
+{/if}
+
+<!--compose sheet (making a message)-->
+{#if $mapStore.composing}
+    <ComposeSheet {lat} {lng} />
+{/if}
+
+
 <style>
 :global(body) {
     margin: 0;
@@ -82,4 +100,25 @@
     color: #666;
 
 }
+
+.fab {
+    position: fixed;
+    bottom: 2rem;
+    right: 1.5rem;
+    width: 56px;
+    height: 56px;
+    border-radius: 50%;
+    background: #111;
+    color: white;
+    font-size: 1.8rem;
+    border: none;
+    cursor: pointer;
+    box-shadow: 0 4px 16px rgba(0,0,0,0.25);
+    z-index: 150;
+    display: flex;
+    align-items:center;
+    justify-content: center;
+    line-height: 1;
+}
+
 </style>
\ No newline at end of file