I love this game! Make sure the participants are bowing their heads and closing their eyes; the-one-who-is-it shouldn't allow the peekers to guess. I also encourage the participants to call each other by name and ask a question (Cindy, do you have the button?) when guessing. It's polite and it gives those who are shy a script to follow. Anyway, there was one boy in my second grade elementary music class years ago who never would speak or sing in class. I often tried to get a sound out of him, but in vain. One day we were playing this game and he had the button. I wondered how he would respond when we all sang, "Who has the button?" We sang it, our heads bowed and eyes closed . . . and in that darkness the sweetest voice sang out clearly and on-pitch, "I have the button!" Yes, I love this game.
If you don't have a button or a key, any objects will do. Also, my classes usually sang this with a triplet/swing feel. I encouraged the university students to maintain a dotted eighth feel and they did pretty well even though a true Scotch Snap (sixteenth followed by dotted eighth) seems to be lost.