Please Turn Your Computer's Speaker "ON"
SET THE TIMER
Step 1: Test the Landing Page. Adjust volume accordingly.
Step 2: Select Hour, Minutes & Seconds then click "Set Timer" button.
Step 3: MINIMIZE this window. Turn monitor OFF (optional)
Test the timer. Set a time about 15 seconds into the future. That way you don't have to wait long to see it operate. At the set time, the landing page will open playing the sound. You may stop the sound by clicking on the "Stop Sound" button or by exiting the page. For your prank, after you set the timer you will have to minimize the timer page and/or turn off the monitor to make the prank "invisible" to your intended victim.
If you don't have access to your friend's computer, then send this page to someone who does (possibly a family member or roommate of your intended victim). Ask them them set the timer for you then wait for the reaction.
Scary, Horror, Spooky