Thread: Computer controlled switches (or Relays)

I apologize if this is answered in a FAQ somewhere... I looked and didn't find it.

My question is: are there computer CONTROLLED switches and relays so I can use my computer to turn on and off devices -- both factory installed and Add-on.

I don't just want my Carputer to run my stereo system, I want it to be able to control anything...

Some examples of what I am looking to do:

• My computer asks for a 5 key pin number, and if it doesn't get it, it shuts down the starter.
  
• I send a message from my handheld to my computer, and it automatically routes my GPS based on the address from my handheld.
  
• When I click the button for my in-dash microphone, the computer turns off the kid's DVD player in the back.
  

I realize that everything that I listed cannot be done by one thing... but I haven't seen anything that showed computer controlled switches which allow me to control add-on devices. Even simple Off/On operation would be a start.

It seems like there are some forward-thinking vendors who have engineered their equipment with software hooks, but what about "dumb" devices like lights, external DVD players, and automatic locks? Are they controllable?