Pictured below is a device branded as “Cure Sleepiness Right Away”, which fits over your ear and lets out a piercing beep when your head tilts forward. Near the bottom of the package, it says:
Especially suitable for long-distance driving, drunk driving and night driving

Photo courtesy of Miss Fipi Lele.
You can see the device in action in the episode of Kenny vs. Spenny shown below, in which Kenny and Spenny’s contest is to see who can stay awake the longest. The device appears at the 2 minute, 44 second mark:






