PsycheDuino

There are many Halloween prop controllers, but I hope mine is the cheapest:

PsycheDuino

Simple iPhone app with six buttons (in the future, possibly more buttons). Also, a screen to edit the text on the buttons.

Pressing a button triggers a signal to be sent to the PsycheDuino box, which will then send a voltage trigger as output.

Here are some more impressive (and more expensive) versions of this idea:

HauntBox