diff --git a/components/copurchase/Copurchase.module.css b/components/copurchase/Copurchase.module.css
new file mode 100644
index 0000000..28a41af
--- /dev/null
+++ b/components/copurchase/Copurchase.module.css
@@ -0,0 +1,120 @@
+.modal {
+  background: #ffffff;
+  width: 456px;
+  border-radius: 10px;
+  border: 1px solid #d8d8d8;
+  box-shadow: 0 4px 24px rgba(0, 0, 0, 0.08);
+  padding: 25px;
+  position: relative;
+}
+
+.closeBtn {
+  position: absolute;
+  top: 17px;
+  right: 17px;
+  width: 16px;
+  height: 16px;
+  border-radius: 2px;
+  border: none;
+  background: transparent;
+  cursor: pointer;
+  opacity: 0.7;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 0;
+  transition: opacity 0.15s;
+}
+
+.closeBtn:hover {
+  opacity: 1;
+}
+
+.header {
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
+  margin-bottom: 20px;
+  padding-right: 24px;
+}
+
+.title {
+  font-size: 17px;
+  font-weight: 700;
+  color: #1a1a1a;
+  line-height: 1.2;
+}
+
+.subtitle {
+  font-size: 13px;
+  color: #666;
+  line-height: 1.4;
+}
+
+.input {
+  width: 100%;
+  height: 36px;
+  border-radius: 8px;
+  border: 1px solid #d8d8d8;
+  padding: 4px 12px;
+  font-size: 13px;
+  color: #444;
+  background: #fafafa;
+  outline: none;
+  margin-bottom: 14px;
+  box-sizing: border-box;
+  transition: border-color 0.15s, box-shadow 0.15s;
+}
+
+.input:focus {
+  border-color: #2e6b8a;
+  box-shadow: 0 0 0 3px rgba(46, 107, 138, 0.12);
+}
+
+.actions {
+  display: flex;
+  justify-content: flex-end;
+  gap: 8px;
+}
+
+.btnPrimary {
+  height: 36px;
+  border-radius: 8px;
+  border: none;
+  cursor: pointer;
+  font-size: 13px;
+  font-weight: 600;
+  padding: 0 20px;
+  background: #2e6b8a;
+  color: #fff;
+  transition: opacity 0.15s, transform 0.1s;
+}
+
+.btnPrimary:hover {
+  opacity: 0.88;
+}
+
+.btnPrimary:active {
+  transform: scale(0.97);
+}
+
+.btnSecondary {
+  height: 36px;
+  border-radius: 8px;
+  border: none;
+  cursor: pointer;
+  font-size: 13px;
+  font-weight: 600;
+  padding: 0 20px;
+  background: #f0f0f0;
+  color: #444;
+  transition: opacity 0.15s, transform 0.1s;
+}
+
+.btnSecondary:hover {
+  opacity: 0.75;
+}
+
+.btnSecondary:active {
+  transform: scale(0.97);
+}
\ No newline at end of file
diff --git a/components/copurchase/CopurchaseInvite.tsx b/components/copurchase/CopurchaseInvite.tsx
new file mode 100644
index 0000000..c996e70
--- /dev/null
+++ b/components/copurchase/CopurchaseInvite.tsx
@@ -0,0 +1,48 @@
+import { useState } from "react";
+import styles from "./CoPurchase.module.css";
+
+interface InviteModalProps {
+  onClose: () => void;
+  onSend: (email: string) => void;
+}
+
+export default function CopurchaseInvite({ onClose, onSend }: InviteModalProps) {
+  const [email, setEmail] = useState("");
+
+  const handleSend = () => {
+    onSend(email);
+    onClose();
+  };
+
+  return (
+    <div className={styles.modal}>
+      <button className={styles.closeBtn} aria-label="Close" onClick={onClose}>
+        ×
+      </button>
+
+      <div className={styles.header}>
+        <div className={styles.title}>Invite to Co-purchase</div>
+        <div className={styles.subtitle}>
+          Invite other labs or colleagues to split the cost of this item.
+        </div>
+      </div>
+
+      <input
+        className={styles.input}
+        type="email"
+        value={email}
+        placeholder="colleague@ucsd.edu"
+        onChange={(e) => setEmail(e.target.value)}
+      />
+
+      <div className={styles.actions}>
+        <button className={styles.btnSecondary} onClick={onClose}>
+          Cancel
+        </button>
+        <button className={styles.btnPrimary} onClick={handleSend}>
+          Send Invites
+        </button>
+      </div>
+    </div>
+  );
+}
\ No newline at end of file
diff --git a/components/copurchase/CopurchaseLabInput.tsx b/components/copurchase/CopurchaseLabInput.tsx
new file mode 100644
index 0000000..a98b39a
--- /dev/null
+++ b/components/copurchase/CopurchaseLabInput.tsx
@@ -0,0 +1,45 @@
+import { useState } from "react";
+import styles from "./CoPurchase.module.css";
+
+interface InviteModalProps {
+  onClose: () => void;
+  onSend: (email: string) => void;
+}
+
+export default function CopurchaseInvite({ onClose, onSend }: InviteModalProps) {
+  const [email, setEmail] = useState("");
+
+  const handleSend = () => {
+    onSend(email);
+    onClose();
+  };
+
+  return (
+    <div className={styles.modal}>
+      <button className={styles.closeBtn} aria-label="Close" onClick={onClose}>
+        ×
+      </button>
+
+      <div className={styles.header}>
+        <div className={styles.title}>Enter your lab</div>
+        <div className={styles.subtitle}>
+          Enter the name of your desired lab
+        </div>
+      </div>
+
+      <input
+        className={styles.input}
+        type="email"
+        value={email}
+        placeholder="Dr. Xu"
+        onChange={(e) => setEmail(e.target.value)}
+      />
+
+      <div className={styles.actions}>
+        <button className={styles.btnPrimary} onClick={handleSend}>
+          Enter
+        </button>
+      </div>
+    </div>
+  );
+}
\ No newline at end of file
diff --git a/models/Notification.ts b/models/Notification.ts
new file mode 100644
index 0000000..98f0992
--- /dev/null
+++ b/models/Notification.ts
@@ -0,0 +1,26 @@
+import mongoose from 'mongoose';
+const { Schema } = mongoose;
+
+const notificationSchema = new Schema({
+    labId: { type: String, required: true },
+    type: { type: String, required: true },
+    resourceId: { type: String, required: true },
+    recipients: [
+        {
+            role: [{
+                type: String,
+                required: true,
+                enum: ["PI", "LAB_MANAGER", "RESEARCHER"],
+            }],
+            channel: [{
+                type: String,
+            }],
+        }
+    ],
+    createdAt: { type: Date, required: true, default: Date.now }
+});
+
+const Notification = mongoose.models.Notification || 
+    mongoose.model('Notification', notificationSchema);
+
+export default Notification;
\ No newline at end of file
diff --git a/models/__tests__/Notification.test.ts b/models/__tests__/Notification.test.ts
new file mode 100644
index 0000000..2addc92
--- /dev/null
+++ b/models/__tests__/Notification.test.ts
@@ -0,0 +1,32 @@
+import Notification from "../Notification";
+
+
+describe("Notification Schema", () => {
+    test("valid user passes", async () => {
+        const notification = new Notification({
+            labId: "lab123",
+            type: "DB_UPDATE",
+            resourceId: "item123",
+            recipients: [
+                {
+                    role: ["PI", "RESEARCHER"],
+                    channel: ["EMAIL"],
+                },
+            ],
+        });
+    await expect(notification.validate()).resolves.toBeUndefined();
+    });
+
+    test("missing required field fails", async () => {
+        const notification = new Notification({
+            type: "DB_UPDATE",
+            recipients: [
+                {
+                    role: ["PI", "RESEARCHER"],
+                    channel: ["EMAIL"],
+                },
+            ],
+        });
+    await expect(notification.validate()).rejects.toThrow();
+    });
+})
\ No newline at end of file
diff --git a/services/__tests__/Notification.test.ts b/services/__tests__/Notification.test.ts
new file mode 100644
index 0000000..365c88c
--- /dev/null
+++ b/services/__tests__/Notification.test.ts
@@ -0,0 +1,55 @@
+import mongoose from "mongoose";
+import { startNotificationWatcher } from "../notifications/watchUpdates";
+import Notification from "@/models/Notification";
+
+jest.mock("mongoose", () => ({
+  ...jest.requireActual("mongoose"),
+  connection: {
+    collection: jest.fn(),
+  },
+}));
+
+jest.mock("@/models/Notification", () => ({
+  __esModule: true, 
+  default: {
+    create: jest.fn(),
+  },
+}));
+
+jest.mock("../../lib/mongoose", () => ({
+  connectToDatabase: jest.fn(),
+}));
+
+const mockCollection = {
+  watch: jest.fn(),
+};
+
+beforeEach(() => {
+  (mongoose.connection.collection as jest.Mock).mockReturnValue(mockCollection);
+});
+
+afterEach(() => {
+  jest.clearAllMocks();
+});
+
+describe("startNotificationWatcher", () => {
+  test("creates notification on update event", async () => {
+    const fakeStream = {
+      async *[Symbol.asyncIterator]() {
+        yield {
+          operationType: "update",
+          fullDocument: {
+            _id: "item1",
+            labId: "lab1",
+          },
+        };
+      },
+    };
+
+    mockCollection.watch.mockReturnValue(fakeStream);
+
+    await startNotificationWatcher();
+
+    expect(Notification.create).toHaveBeenCalled();
+  });
+});
\ No newline at end of file
diff --git a/services/notifications/index.ts b/services/notifications/index.ts
new file mode 100644
index 0000000..55ec001
--- /dev/null
+++ b/services/notifications/index.ts
@@ -0,0 +1,4 @@
+import { startNotificationWatcher } from "./watchUpdates";
+
+// Entry point for notification service
+startNotificationWatcher();
diff --git a/services/notifications/watchUpdates.ts b/services/notifications/watchUpdates.ts
new file mode 100644
index 0000000..a1fa716
--- /dev/null
+++ b/services/notifications/watchUpdates.ts
@@ -0,0 +1,37 @@
+import mongoose from "mongoose";
+import { connectToDatabase } from "@/lib/mongoose";
+import Notification from "@/models/Notification";
+
+/**
+ * Starts a Change Stream watcher on the "products" collection.
+ * Inserts a DB_UPDATE notification whenever a product is updated.
+ */
+export async function startNotificationWatcher() {
+  await connectToDatabase();
+
+  const collection = mongoose.connection.collection("items");
+
+  const changeStream = collection.watch([], {
+    fullDocument: "updateLookup",
+  });
+
+  for await (const change of changeStream) {
+    if (change.operationType !== "update") continue;
+
+    // Get the updated document from the change stream
+    const updatedDoc = change.fullDocument;
+
+    // If there’s no document, skip this iteration
+    if (!updatedDoc) continue;
+
+    // TODO: Check the quantity in updatedDoc
+    // If quantity is below the threshold, continue
+    // Otherwise, send a notification
+    await Notification.create({
+      type: "DB_UPDATE",
+      labId: updatedDoc.labId ?? "unknown",
+      resourceId: String(updatedDoc._id),
+      recipients: [],
+    });
+  }
+}