I know I am been thick, but

[Paul_B]

Okay I want to keep my existing light switches and introduce automation systems in parallel. So someone switches on a light switch the HA knows about it, but I can also control the lighting circuit through HA. How can I do this?

Do I just monitor the currant increase when the light-switch is turned on and interpret this as digital on (5v)?

[toscal]

Re: I know I am been thick, but

Quickest and possibly the cheapest is to use X10 2way appliance modules. Such as the AWM2 Micromodule. This Module fits behind the wall switch, and when you tum on the light via the switch it will also transmit this fact to the HA controller.
On controlers do you want PC based or stand alone.
For stand alone you can't beat the Homevision system from CSI www.csi3.com
Another one to look at is the Ocelot, not as easy to program but it is cheaper. www.appdig.com/adicon_new/index.htm

For PC based I would go for Homeseer, it is very good. www.homeseer.com
Oh be careful there are cheaper micro modules but many are not 2 way. And if you need your HA controller to know what is on, when you switch a light on manually, then 2 way is what you need.