It's easily to make the simple classroom quiz buzzers .I use a switch,two Electronic stopwatches(including batteries),four meters wire and some electric tools.It's a parallel circuit.
But it has low accuracy.

Forgive my ignorance. I searched Google with <em><strong>responder</strong></em> but I could not found what thing it is. Can you explain it to me?
I think it's basically one of those things where two people are asked a question. When one of the two thinks they know it, they press their respective button and get to answer their question. This tells who the first person to press their button was.
you are right.so,can you tell me what it is in English?Google tells me that it is a responder.all in all,thanks for your help.
They are often called classroom quiz buzzers. Here is a link with a lot of different ones. http://www.trainerswarehouse.com/products.asp?dept=122
Thanks, seraine. I see that is a very clever solution to a trivial problem.
Thanks again.
Thanks, seraine.
I feel sorry that my english is not good to explain what it is.it calls &aelig;Š&cent;&ccedil;&shy;”&aring;™&uml; in Chinese.it also calls competitive answer machines.It's used to determine who can answer in advance. Thanks for your reminding. <br>

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