Your download is starting
If nothing happened, start it by hand — then follow the three steps below.
macOS will block the first launch
You will see “Air Mouse cannot be opened because the developer cannot be verified.” That is Gatekeeper reporting the absence of a paid Apple Developer ID, not a problem it found with the app.
To open it anyway: right-click Air Mouse in your Applications folder and choose Open, then confirm. Double-clicking will not offer the choice — the option only exists in the right-click menu. You only have to do this once.
The source is public, and every release is built by GitHub Actions from a tagged commit, so you can check what went into the build rather than taking the download on trust.
Then three steps
Move it to Applications
Open AirMouse.dmg and drag Air Mouse onto the Applications shortcut in the window that appears.
Allow it to control your Mac
Moving the cursor and typing counts as controlling your Mac, so macOS asks for Accessibility permission. The setup window walks you through it and continues on its own once the switch is on.
Scan the code
A QR code and a six-digit PIN appear. Point your phone's camera at the code, enter the PIN once, and the trackpad opens in the browser.
When you first open the page on your phone, the browser warns about the certificate. That is expected: the connection is encrypted with one your Mac generated for itself, which no public authority can vouch for. Tap Show Details, then Visit this Website.