After I run my code, you'll see that in the result, my title is changed and the last modified information is still the same.

One last thing. SystemUpdate also takes a boolean parameter. By default, the value is false; however, if you set it to true, the version number of your item will increment. If you choose to make the change and increment the version number using SystemUpdate(true), the last modified information will still remain the same and you still will not trigger an alert.