diff --git a/docs/embed-sdk/v0.md b/docs/embed-sdk/v0.md
index c415d40..9b3d2ab 100644
--- a/docs/embed-sdk/v0.md
+++ b/docs/embed-sdk/v0.md
@@ -175,6 +175,27 @@ const rkey = uri.split('/').pop();
 Blento.notifyNavigate(`/${session.did}/event/r/${rkey}`);
 ```
 
+### `Blento.promptLogin(): void`
+
+Ask the parent to show its login modal. Fire-and-forget — there is no
+returned Promise. To detect when the user has signed in, subscribe to
+`session` events:
+
+```js
+if (!Blento.getSession()) {
+	const off = Blento.on('session', (s) => {
+		if (s) {
+			off();
+			doTheThing();
+		}
+	});
+	Blento.promptLogin();
+}
+```
+
+Calling `promptLogin()` while the user is already signed in is a no-op from
+the iframe's perspective; the parent may still display the modal.
+
 ## Errors
 
 All write rejections are `BlentoError` instances with a stable `.code`:
@@ -213,8 +234,9 @@ implement directly. All messages include `v: 0`.
 { v: 0, id, type: 'deleteRecord', payload: { collection, rkey } }
 { v: 0, id, type: 'applyWrites',  payload: { writes, validate? } }
 { v: 0, id, type: 'uploadBlob',   payload: { bytes: number[], mimeType } }
-{ v: 0,     type: 'blento:resize',   heightPx }                // unsolicited
-{ v: 0,     type: 'blento:navigate', url }                     // unsolicited
+{ v: 0,     type: 'blento:resize',      heightPx }             // unsolicited
+{ v: 0,     type: 'blento:navigate',    url }                  // unsolicited
+{ v: 0,     type: 'blento:promptLogin' }                       // unsolicited
 ```
 
 `id` is any unique string you generate — the parent echoes it on the response.
diff --git a/src/lib/embed/AtmoEmbed.svelte b/src/lib/embed/AtmoEmbed.svelte
index 7f4ed2c..7cc3490 100644
--- a/src/lib/embed/AtmoEmbed.svelte
+++ b/src/lib/embed/AtmoEmbed.svelte
@@ -3,6 +3,7 @@
 	import { browser } from '$app/environment';
 	import { page } from '$app/state';
 	import { user } from '$lib/atproto';
+	import { atProtoLoginModalState } from '$lib/atproto/LoginModal.svelte';
 	import {
 		embedApplyWrites,
 		embedCreateRecord,
@@ -201,6 +202,11 @@
 			return;
 		}
 
+		if (data.type === 'blento:promptLogin') {
+			atProtoLoginModalState.show();
+			return;
+		}
+
 		if (typeof data.id === 'string' && typeof data.type === 'string') {
 			handleRequest(data.id, data.type, data.payload);
 		}
diff --git a/static/embed/v0/sdk.js b/static/embed/v0/sdk.js
index 5ad79d0..1ab4bd6 100644
--- a/static/embed/v0/sdk.js
+++ b/static/embed/v0/sdk.js
@@ -14,8 +14,9 @@
  *   { v: 0, id, type: 'deleteRecord', payload: { collection, rkey } }
  *   { v: 0, id, type: 'applyWrites',  payload: { writes, validate? } }
  *   { v: 0, id, type: 'uploadBlob',   payload: { bytes: number[], mimeType } }
- *   { v: 0,     type: 'blento:resize',   heightPx }
- *   { v: 0,     type: 'blento:navigate', url }
+ *   { v: 0,     type: 'blento:resize',      heightPx }
+ *   { v: 0,     type: 'blento:navigate',    url }
+ *   { v: 0,     type: 'blento:promptLogin' }
  *
  * ─── Wire protocol (parent → iframe) ─────────────────────────────────────────
  *   { v: 0, type: 'ready', session }                      // sent once after handshake
@@ -202,6 +203,9 @@
 		},
 		notifyNavigate: function (url) {
 			sendToParent({ v: PROTOCOL_VERSION, type: 'blento:navigate', url: url });
+		},
+		promptLogin: function () {
+			sendToParent({ v: PROTOCOL_VERSION, type: 'blento:promptLogin' });
 		}
 	};
 
diff --git a/static/embed/v0/test.html b/static/embed/v0/test.html
index 44e8e4e..19b652d 100644
--- a/static/embed/v0/test.html
+++ b/static/embed/v0/test.html
@@ -130,6 +130,7 @@
 		<div class="row">
 			<button id="btn-resize">notifyResize(800)</button>
 			<button id="btn-navigate">notifyNavigate('/')</button>
+			<button id="btn-prompt-login">promptLogin()</button>
 		</div>
 
 		<div class="field">
@@ -249,6 +250,11 @@
 				show('notifyNavigate(/) sent', null);
 			};
 
+			$('btn-prompt-login').onclick = () => {
+				window.Blento.promptLogin();
+				show('promptLogin() sent', null);
+			};
+
 			if (window.Blento.getTheme().dark) {
 				document.documentElement.classList.add('dark');
 			}