It's really not that kinda trick, to answer DaveV's question as well, it is a lie detector test where the volunteer holds a lantern and you ask them questions and the lantern beeps whenever they "lie". You eventually get around to discovering what the persons card is by asking "was your card black?" etc. if they lie you make the lantern buzz. Thankfully, seeing as there seems to be no way around the noisy remote, its one of those tricks where, like the first time i saw it performed, you know how it works. Everyone i saw it with knew that the comedian/magician had a remote. But the banter and asking questions (aka "would you like to kiss someone other than your wife tonight? "no" BUZZ etc.) going up to the trick was so funny that the audience really didn't care. Guess I'll just have to be funny.
Well, you basically answered your question. Based on how you described it, the audience can see what you do without it spoiling the trick due to the comedic element involved. However, if you do want to keep it 'secret', you could use any buzzer you want, just make sure that the clicker is silent (unless you specifically need a specially bought gimmicked buzzer). I can't vouch for this myself as I have never tried it, but you can probably find a buzzer at most electronic stores (Radioshack or Circuit City spring to mind).