How do I check if button pressed?

Hello, happy 2007.

I have five buttons, only one of these will allow the user to start a demo.

I need to let the user know when they have pressed the wrong button and indicate that with an alert message…if they make another error I need to show a different alert message.

How do I let the ‘wrong’ buttons know that one of them has been pressed incorrectly therefore if pressed again will show the second alert message?

Many thanks