diff --git a/README.md b/README.md
index 7a392e2..df6887c 100644
--- a/README.md
+++ b/README.md
@@ -230,9 +230,47 @@ run, so releases cannot loop. For a MINOR or MAJOR release, bump the version
 yourself (`npm version minor --no-git-tag-version`) and push; the next patch bump
 continues from there.
 
-macOS builds are unsigned by default. To sign and notarise, set
-`CSC_LINK`/`CSC_KEY_PASSWORD` and the notarisation credentials before running
-`npm run dist:mac`.
+### Unsigned macOS builds
+
+macOS builds carry no Apple certificate. `electron-builder.yml` sets
+`identity: "-"`, and `dist:mac` runs with `CSC_IDENTITY_AUTO_DISCOVERY=false`, so
+a certificate sitting in your keychain is never picked up — a build on your
+machine is byte-for-byte the same deal as a build in CI.
+
+`"-"` is an *ad-hoc* signature: no identity, no team, nothing Gatekeeper will
+accept — but a structurally valid one. That is the part worth having. Skipping
+signing altogether leaves the bundle carrying Electron's original signature over
+resources electron-builder has since rewritten, which `codesign --verify` fails:
+
+```
+code has no resources but signature indicates they must be present
+```
+
+A quarantined app in that state is not merely refused — Gatekeeper reports it as
+"damaged and can't be opened. You should move it to the Trash", and right-click →
+*Open* will not get past it. With a valid ad-hoc signature the same app gets the
+ordinary unidentified-developer dialog instead, which right-click → *Open* does
+clear.
+
+So the `.app` runs anywhere, but macOS quarantines it the moment it arrives by
+download, AirDrop, Slack or email, and an ad-hoc signature does not clear that
+quarantine. Whoever you hand the build to has to say so once, either way:
+
+- **Finder** — right-click the app, choose *Open*, then *Open* in the dialog.
+  On macOS 15 and newer, open it normally first, then allow it under
+  *System Settings › Privacy & Security*.
+- **Terminal** — strip the quarantine flag outright:
+
+  ```bash
+  xattr -dr com.apple.quarantine "/Applications/Mongo Explorer.app"
+  ```
+
+Either is needed only once per install, not per launch.
+
+To ship something that skips all of this, sign and notarise properly: set
+`CSC_LINK`/`CSC_KEY_PASSWORD` and the notarisation credentials, drop the
+`identity` line from `electron-builder.yml`, and set `hardenedRuntime: true`
+(notarisation requires it) before running `npm run dist:mac`.
 
 ## Verifying
 
diff --git a/electron-builder.yml b/electron-builder.yml
index a7de408..27f0512 100644
--- a/electron-builder.yml
+++ b/electron-builder.yml
@@ -38,8 +38,15 @@ mac:
     - target: zip
       arch: [arm64, x64]
   darkModeSupport: true
-  # Unsigned local builds: without this macOS refuses to open the .app because
-  # the hardened runtime has no signature to validate.
+  # No Apple certificate is ever used. "-" is an ad-hoc signature: it carries no
+  # identity, so the app stays unsigned as far as Gatekeeper is concerned, but it
+  # is a *valid* one. Without it the bundle keeps Electron's own signature over
+  # resources we have since rewritten, and Gatekeeper calls a quarantined copy of
+  # that "damaged" — which right-click Open cannot clear, unlike an ad-hoc build.
+  identity: "-"
+  # The hardened runtime would validate that signature against an identity there
+  # isn't one of, and gatekeeperAssess would run the build through spctl, which
+  # by definition rejects anything unsigned.
   hardenedRuntime: false
   gatekeeperAssess: false
   extendInfo:
diff --git a/package.json b/package.json
index 4be4418..6cf6c6d 100644
--- a/package.json
+++ b/package.json
@@ -22,7 +22,7 @@
     "smoke": "node scripts/build-smoke.mjs && node scripts/with-mongod.mjs electron dist/smoke/smoke.js",
     "pack": "npm run build && electron-builder --dir",
     "dist": "npm run build && electron-builder -mwl",
-    "dist:mac": "npm run build && electron-builder --mac",
+    "dist:mac": "npm run build && CSC_IDENTITY_AUTO_DISCOVERY=false electron-builder --mac",
     "dist:win": "npm run build && electron-builder --win",
     "dist:linux": "npm run build && electron-builder --linux",
     "ui-check": "npm run build && node scripts/build-ui-check.mjs && node scripts/with-mongod.mjs electron dist/smoke/ui-check.js",