doorbell camera/intercom

[ddl@danlan.*com (Dan Lanciani)]

I'm having a few exterior doors replaced/rebuilt and I thought I'd
take this opportunity to install some more gadgets while the walls
are open.  There are many doorbell camera/intercom units that talk
over a single pair of wires (presumably to make it easy to replace
a conventional button) but they seem to be pretty much closed systems.
I saw one with a video output from the master panel, but it wasn't
clear when it was active.  I'd like to have standard video available
at all times and a regular contact closure button.  Anybody know of
a (possibly older) system whose door-mounted component works this way?
If not I'll just mount a separate camera, but some of the integrated
devices look better...

				Dan Lanciani
				ddl@danlan.*com