Need multiplayer game buzzer schematic

Factual Questions
1

The title pretty much says it all. I know the subject has come up before, but it was a while ago and I can’t seem to find it.

I’ve got a sci-fi convention coming up in five weeks and I’d like to have a buzzer allowing four or more players to “ring in” for a trivia contest. Help much appreciated, thanks.

2

I haven’t tried to build this one, and can’t say much about it except that on a quick glance it looks like it might work.

http://andy.babylonia.flatirons.org/tech.php

3

Thanks, but that design involves relays, which can get kinda pricey. Is there a solid-state version?