> I am trying to implement several remote keypads with one central master,
> very similar to a home security system.  Each keypad uses a 4x4 matrix
> keypad, a 16x2 backlit LCD, 3 diodes, a piezo buzzer, and 2-wire serial
> communications with the master.


I would put a processor in each keypad, and go for otherwise, minimum parts.

Make sure to protect your comm lines with something robust, like 232 drivers
or similar. If you take alarm wiring directly to the processor (including
sensors) you will discover the pain that the alarm industry went through in
the late 70s, early 80s.