In this instructable I will show you one of the many ways to freak someone out with a party popper!
Warning: low quality pictures :(
First, you take the party popper and pull all the streamers out.
You then cut it (as shown). Try to trim the popper as close as you can to the plastic cylinder surrounding the powder roll.
Take the string and tie a knot in it, near the end.
You then take the popper string and tie the string just above the previous knot, so that when pulled, it will catch on the knot.
Take a strip of duct tape and lay it across the party popper tube, avoiding contact with the string.
Attatch a strip of duck tape across the end of the string that will be taped to the door.