Is it possible to have machines, like for example, door switches, work in multiplayer?

Yes, but to sync their positions, it would require a biped crush script.

What's that?

A script that uses biped deaths as booleans.

What sort of format would I use to set up this particular script? The commands are what I'm looking for...at least an example of one.

protip: don't try to sync devices online. It won't turn out the way you're expecting it and it causes lag to use the biped crush method (and the last thing CE MP needs is more lag ._.)
Fast moving doors based on player position are ok, but even those can cause problems, if a player shoots a rocket, it might hit the door on one player's screen but miss the door on another player's screen, because the position of the door isn't transferred across the connection between clients (as far as I know)

Thanks guys.

If doors open and close automatically when a player gets near them, it syncs just as well as the covy shields. Since the player's position syncs, the automatic doors would "sync."