Most stunts tend to happen with pass rushers who are next to each other, and they use their rush path to catch linemen off guard. The Hi-Lo stunt, however, takes place between edge rushers on either side of the formation, and it’s designed to catch an unsuspecting quarterback.
You can see a great example from the Super Bowl champion Seahawks below. First, watch Demarcus Lawrence (#0) and Boye Mafe (#53) signal to each other before the snap:
The stunt was on.