Short answer: Cmd Q sits next to Cmd W and Cmd Tab, so a slip quits the whole app. There are three common guards. Press twice asks for a second Cmd Q within a moment. Confirm puts up a dialog you answer. Hold makes you keep Cmd Q down for about two thirds of a second. Hold is the quietest for a fast typist, press twice works everywhere Still Dock runs, and a confirmation is the clearest for someone who is new to a Mac.
| Press twice | Confirm | Hold | |
|---|---|---|---|
| What you do to quit | Press Cmd Q, then press it again quickly | Press Cmd Q, then click Quit in a dialog | Keep Cmd Q held down for a moment |
| What a slip does | Shows a short hint and nothing quits | Opens a dialog you have to close | Shows a short hint and nothing quits |
| Hands stay on the keyboard | Yes | Yes, with Return or Escape | Yes |
| Easy to explain to someone new | Yes | Yes, the dialog says what happens | Takes one try to learn |
| Where you find it | Still Dock, both versions | Some apps' own settings, such as Firefox | Chrome's Warn Before Quitting, Still Dock from stilldock.com |
The first Cmd Q shows a hint over the Dock, "Press Cmd Q again to quit", and the app keeps running. A second press within a moment quits as normal. A fast double tap still quits, so this suits people who quit apps often and want the guard to stay out of the way. It is the style the App Store version of Still Dock uses, and you can choose it in the version from stilldock.com too.
A dialog asks whether to quit. Nothing can quit by a stray key press while the dialog is open, and the words say exactly what is about to happen, which helps a child or an older parent. The cost is one more click or Return every time you mean it. Some apps offer this for themselves; Firefox, for example, can ask before Cmd Q quits. Still Dock uses a confirmation for Cmd W in the version from stilldock.com, where closing a window by a slip is the bigger risk.
Holding Cmd Q for about two thirds of a second quits; a quick press does nothing but show a hint. Chrome made this familiar with Warn Before Quitting. It costs a fast typist almost nothing, because a deliberate quit is a slightly longer press. Still Dock offers hold in the version from stilldock.com, for any app you choose. Holding a key down for another app needs Accessibility permission, so the App Store version offers press twice.
Cmd Q protection is part of Still Dock Pro. For more on the guard itself, see how to disable Cmd Q on a Mac.
All three stop a single slip. Confirm is the hardest to get past by accident, because it waits for an answer. Press twice and hold let a deliberate quit through without a dialog.
Yes. Choosing Quit from an app's menu is always allowed. Only the Cmd Q keys are guarded.
Still Dock guards the apps you add to its list. Still Dock itself always quits with a single Cmd Q, so it can never trap you.