Whenever the fans in my MacBook Pro suddenly rev up, I use the built-in Activity Monitor app (Applications > Utilities) to see what’s going on. But I’ve often wished for a quicker and easier way to check my Mac’s activity than having to open Activity Monitor.
The free System Lens (Mac App Store link) offers a compromise: It resides in the menu bar, and when you click its icon, you see a snapshot of which apps are actively using your computer’s resources.
System Lens doesn’t offer all the features or the flexibility of Activity Monitor. For example, while Activity Monitor provides hard numbers about how much processing power an app is using (such as CPU percentage or the number of threads), System Lens uses simple labels: Low, Medium, and High. For people who want the details, System Lens won’t replace Activity Monitor completely.
(These Low, Medium, and High indicators represent numerical ranges of CPU percentage. For example, System Lens’s default range for the Low category is 1 to 20 percent, so if Activity Monitor shows that Safari Web Content is using 15 percent of your CPU resources, System Lens would categorize that process as Low. You can customize the Low, Medium, and High ranges, which is helpful if you’re familiar with the demands of your apps and you want System Lens to better reflect your workflows.)
Similarly, while Activity Monitor lets you Quit or Force Quit an app, System Lens gives you only the option to Force Quit—in the System Lens popover, you click an app’s name, and then click the terminate (x) button that appears. A Force Quit abruptly shuts an app down without a chance to save your work, so if you want to “gently” quit an app to free up processor resources, preserving any unsaved changes you’ve made, you should quit the app normally, rather than from within System Lens.
But System Lens’s simplicity can also be a benefit. Activity Monitor’s list of processors includes everything that’s running on your computer, including background processes, so the list is long—and contains many items you shouldn’t quit. By default, System Lens shows only foreground apps—the apps most people are likely to be concerned with—and even then, it shows by default only those foreground apps currently using at least 1 percent of CPU resources. In other words, System Lens’s list won’t show you a long list of apps that aren’t currently doing anything.
If you want to omit a particular app from the list—say, an app that always uses roughly the same amount of processor resources, so you don’t care to monitor it—you can create a filter for that app in System Lens’s preferences window.
To prevent System Lens itself from using too much of your processor resources, the utility displays only snapshots of your system—the list of apps and their usage isn’t updated in real time. The result is that System Lens’s display can be very different from one click of the utility’s menubar icon to the next. This means you can’t use System Lens to monitor processor usage over a period of time, but it’s useful for seeing what’s happening at a given moment. (Older Mac App Store reviews complained that System Lens itself took up too many processor resources. According to the developer, the current version fixes this issue. I never saw System Lens take up more than 1 percent of my CPU resources in my testing.)
System Lens is limited, but if you want to see your processor activity on a very basic level, the app provides a quick, easy to view list of apps and their impact. It’s free, so there’s little risk in giving it a try.