BusyCal relies on its BusyCal Menu app extension to issue alarms. This extension gets bundled and installed as part of the main app.

There is a known issue in macOS where at times the wrong extension may get loaded (from another installed copy on disk, or even at times from a Time Machine backup) and due to this, alarms may stop working as the main app is unable to communicate with the menu extension.

You can easily fix this problem by performing these steps:

• Select BusyCal > Preferences > General, and uncheck "Show BusyCal Menu in menu bar".
• Select BusyCal > Preferences > Alarms, and uncheck "Show alarms".
• Quit/relaunch BusyCal.
• Select BusyCal > Preferences > General, and check "Show BusyCal Menu in menu bar".
• Select BusyCal > Preferences > Alarms, and check "Show alarms". Make sure you then have Use BusyCal Alarm Window selected

In case alarms still do not work, check to ensure macOS has loaded the correct version of BusyCal Menu:

• Launch Activity Monitor.app
• Find "BusyCal Menu" and click on the (i) information button in the top left corner of the toolbar.
• Click on "Open Files and Ports".
• You will see a lot of opened files listed. Make sure the extension is loading from "/Applications/BusyCal.app/...".

If you see some other unknown path, such as the downloads folder or a Time Machine backup on an external drive, you will need to navigate to that path and delete the app. You can also spotlight for "BusyCal.app" and delete any duplicate copies found on disk (including your Downloads folder).

This way, macOS will only find a single copy installed and choose to launch the extension from the correct location.

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