It may be easier to go with the Pronto. You could have a button for the VCR, DVD, and Cable on the front, which would bring you to the controls for that unit. You also have the option of write protecting it.

I agree with Greg, discrete codes are a must.

As far as security, you may want to look at some of the wired security products for computers. They basically have a signal cable attached to the computer. If the connection is broken, an alarm goes off. I'm not sure what you would do if there weren't reliable staff there during the same hours as the customers.

Also, this would be IR control, not serial.

CJ