Need help with the best prank ever?

Tonight at 12:00 I'm going to play a ginormous prank on my mom and my sisters. We live out in the country in missouri so I've got alot of room. I strung a very long wire from one tree to the other (about 200 feet across and about 20 feet high) and I'm going to hang a light (it has like 5 different colors) from this wire. It's going to look alot like there is a UFO floating in the air. I also have a HUGE (concert size) speaker and I'm going to put it behind our shed and play a VERY loud sound of a very high pitched frequency wave. I will also have a very thick cloud of smoke that will envelop the whole scene. But I have a couple questions... How should I go about making a huge cloud of smoke? And how should I end it? (the light automatically turns off after 1 hour). What should I do to make it more believable? And just what could I do to improve it? This is hopefully gonna be AWESOME! thanks guys!