The six month prank

The setup: 

The base for our cordless phone is in the same room that our personal gym is in. On said phone base there is a "page headset" button. When you push that button, the headset (which we keep in the living room) starts ringing very loudly and nonstop until you hit its off button.

Kim knows not of this button.

The execution:

About six months ago, I was working out in the gym room with the door closed and the music blasting while Kim was in the living room. Then I had a great idea. I would push the button every few minutes and see what Kim does. After the fourth or fifth time, she came into the room to ask me if I knew why the phone was all jacked up. Somehow I was able to keep a straight face while I asked her what it was doing and said that I had no idea what was up. She went back into the living room and I pushed the button a couple more times before finishing my workout.

About two months later I pull the same stunt. Kim comes in and says it's doing it again, and again I'm able to keep a straight face. When I come back out of the room, the phone is still ringing, but it's all muffled. Kim had put a blanket over it because she was sick of pushing the off button over and over again.

Flash forward to just a few days ago:

Same thing as the other two times, Kim's all frustrated with the phone randomly ringing every couple of minutes, I play dumb. At this point I decide it's time let her in on the prank. I start dropping little hints like telling her that it's strange that it only ever does it when i'm doing my workout and she's in the living room. She doesn't pick up on this. So I start pushing the button and then immediately come out to hit the off button. Still nothing from Kim. Now, there's about a two or three second delay from when I push the page button until the headset actually starts ringing, so I get to the point where I push it and then run out to the living room a split second before it start ringing so I can turn it off a quick as possible. I do this about 15 times in a minute before Kim tells me to just forget about it and let it ring. Keep in mind that my music in the gym room has been blasting and there's no possible way I could have even heard the phone ringing from in living room, not to mention that I haven't been able to keep my face straight anymore and am about to explode with laughter. I am absolutely amazed that Kim has not figured this out yet, especially since it's usually very hard to pull one over on her. I was actually thinking of prolonging the joke, but I didn't think I'd be able to do anything grander that what I had just done. So at the end of my workout I call her into the gym room and tell her that I think I figured out what was wrong with the phone. I ask her if she sees the page button on the base. She says yes but apparently still has no clue what's going on. So I tell her that it seems like the phone only rings every time I push that button. Her face is blank and expressionless for about 5 seconds (I'm staring at her with a huge smile on my face) and then it hits her all at once. I can tell she wants to be mad at me, but neither of us can stop laughing our asses off. 

She finally admits that it was probably the best prank ever pulled on her, then spends the rest of the night pouting and calling herself retarded.