Gatekeeper is a security feature introduced in macOS in Mountain Lion that let users choose which apps can and can not run on their Macs. The feature has three options for allowing/disallowing apps; run apps from the Mac App Store only, run apps from the Mac App Store and from identified developers, and run apps from anywhere i.e. from any origin and developed by anyone. To run apps from unverified developers, you have to change Gatekeeper’s settings and allow apps to run from anywhere and then you have to remember to change the setting back if you want to keep your system safe. Alternatively, macOS does let you run just the one app as an exception and keep the Gatekeeper settings unaltered. Here’s how.
Let’s say you downloaded an app from outside the Mac App Store and it is from an unidentified developer, or that this particular app hasn’t been signed. El Capitan will not let it run but you know that the app is safe and would like to run it anyway. On the surface of it, there doesn’t seem to be a way to do that from the prompt you get when you try to run the app. You need to look elsewhere.
Open System Preferences and go to Security & Privacy. Click the padlock button at the bottom to unlock the settings for Gatekeeper. You may be asked to enter your password. You will see the usual three options for allowing/disallowing apps but you will also see a new addition; the app that was just prevented from running will be listed here with an ‘Open Anyway’ button. Click it, enter your password when/if prompted and the app will be allowed to run.
Gatekeeper’s settings remain unchanged and any time you need to run the same app, you will be able to do so without Gatekeeper ever stopping you.
It’s worth mentioning that Windows 10 has similar protection enabled that prevents unverified apps from running but allowing them to run as an exception is much simpler with the option present on the Smartscreen alert itself.