diff --git a/README.md b/README.md
index 83eedc5..1c5dd56 100644
--- a/README.md
+++ b/README.md
@@ -23,7 +23,7 @@ Sleep prevention is an OS-level assertion, so the extension delegates to the pla
 
 | Platform | Mechanism |
 | --- | --- |
-| macOS | `/usr/bin/caffeinate -i [-d] [-s]` |
+| macOS | `/usr/bin/caffeinate -i [-d] [-s]` (defaults to `-i -d`) |
 | Linux | `systemd-inhibit --what=idle:sleep --why=<reason> sleep infinity` |
 
 Both run until signalled — there is no timer, so nothing needs to be refreshed or babysat.
@@ -63,7 +63,7 @@ pkill -f vicinae-caffeinate
 
 | Preference | Default | Notes |
 | --- | --- | --- |
-| Also Prevent Display Sleep | off | macOS only. `systemd-inhibit` cannot hold the display awake — that is the compositor's job, and the UI says so rather than pretending. |
+| Prevent Display Sleep | **on** | macOS only. On by default: `caffeinate -i` alone blocks *system* idle sleep, so the screen still blanks and the extension looks broken. Turn it off to save battery. `systemd-inhibit` cannot hold the display awake — that is the compositor's job, and the UI says so rather than pretending. |
 | Also Prevent System Sleep | off | On macOS this assertion only takes effect while on AC power. |
 
 ## Development
diff --git a/package.json b/package.json
index 08955a8..f54db8f 100644
--- a/package.json
+++ b/package.json
@@ -26,12 +26,12 @@
   "preferences": [
     {
       "name": "preventDisplaySleep",
-      "title": "Also Prevent Display Sleep",
-      "description": "Keep the screen on as well. Off means the display may still turn off while the system stays awake.",
+      "title": "Prevent Display Sleep",
+      "description": "Keep the screen on. On by default, because a blank screen is the usual reason caffeination looks like it is not working. Turn it off to let the display sleep while the system stays awake (saves battery).",
       "type": "checkbox",
       "label": "Prevent display sleep",
       "required": false,
-      "default": false
+      "default": true
     },
     {
       "name": "preventSystemSleep",
diff --git a/src/__tests__/manifest.test.ts b/src/__tests__/manifest.test.ts
new file mode 100644
index 0000000..4f4b656
--- /dev/null
+++ b/src/__tests__/manifest.test.ts
@@ -0,0 +1,46 @@
+import { readFileSync } from "node:fs";
+import { join } from "node:path";
+
+import { describe, expect, it } from "vitest";
+
+import { flagsFromOptions } from "../lib/platform";
+import { CaffeinateOptions } from "../lib/types";
+
+interface Preference {
+  name: string;
+  default?: unknown;
+}
+
+const manifest = JSON.parse(readFileSync(join(process.cwd(), "package.json"), "utf8")) as {
+  preferences: Preference[];
+};
+
+function preferenceDefault(name: string): unknown {
+  return manifest.preferences.find((preference) => preference.name === name)?.default;
+}
+
+/**
+ * `caffeinate -i` blocks *system* idle sleep but lets the display blank, which
+ * is the #1 way this extension looks broken: the screen sleeps, so the user
+ * concludes the toggle did nothing. Display sleep prevention must stay on by
+ * default; opting out is a deliberate battery-saving choice.
+ */
+describe("manifest defaults", () => {
+  it("prevents display sleep by default", () => {
+    expect(preferenceDefault("preventDisplaySleep")).toBe(true);
+  });
+
+  it("leaves full system sleep opt-in", () => {
+    expect(preferenceDefault("preventSystemSleep")).toBe(false);
+  });
+
+  it("maps the shipped defaults onto flags that keep the screen awake", () => {
+    const defaults: CaffeinateOptions = {
+      preventDisplaySleep: preferenceDefault("preventDisplaySleep") as boolean,
+      preventSystemSleep: preferenceDefault("preventSystemSleep") as boolean,
+    };
+
+    // "id" == -i -d: idle sleep AND display sleep both blocked.
+    expect(flagsFromOptions(defaults)).toBe("id");
+  });
+});