How to change the property of an object when user says (x)?

Looking on making a sort of game that has certain elements when you need to say something in order for a door to open.

But, I was also wondering if there was a way to make it so it can only be activated from a certain amount of bricks away. Because, if someone has been on the server before, they can ruin it for the people by saying the word right when they spawn, when they're miles away from the door.

So, this is what I need:

A script that changes the property of a brick when user says (x). A second part to this script that won't allow the brick to change properties if they're not close enough.

I can do without the second part, but I'd really prefer if it would go with it. Dunno if it's not possible.

Cheers,