Now this will not be cheap, but it will be industrial grade and last the lifetime of the house. You will need to do your own wiring and your own programming. If you have basic skills of pulling cat-5 cable and basic home wiring skills, you can do this your self.
You can do this for about $250 and a few weekends worth of your time. You can spend about that much and have a toy system or go this route and have an industrial system.
You will need to start with a parts list.
First, you will need a board to switch everything. Start here.... http://www.ebay.com/itm/OPTO-2...
This board already has some 120v output switching. $31 at current price, there are cheaper that you can find still. But what this board doesn't have is the 120v input modules, they are yellow... Here is a lot of input and output.... http://www.ebay.com/itm/4-Opto...
You still should be able to find them cheaper.
You are going to need a 1000 foot roll of 4 pair 18 guage wire with wire colors white, black, red, green. This is an industry standard... http://www.ebay.com/itm/18-Gau...
Start with that. Depending on your building codes if you can prove that you pulled this wire and it had been there for 5 or more years, you will not have to pull it out when you sell your home.
Now the fun part. You need to find a central location in your home to mount the G4PB24 board and possible others when you expand the system. This place need space to have a computer and a connection to the internet too.
Start with the light switches. You will need to run your wire from your central location to your light switches. Pull off the plate to the switch and run your wire in the wall to this switch. The switch will have two wires connected to it. One from power and one going to the light fixture.
The black wire(in the US) from the power line is connected to to the bottom of the switch.
Connect the black wire from the 4 wire cable you pulled and connect it there with the black wire to power. Do not remove the black power line wire from the light switch.
Disconnect the black wire that runs to the light fixture and wire nut it to the red wire in the 4 wire pair that you pulled.
Connect the Green wire to the switch where you removed the black wire from the switch. The Green wire will carry the switch power.
The white wire from both power and light fixture should be wire nutted together. Add the white wire from the 4 pair wire to those 2 wire nutted. That is your neutral.
Now on the G4PB24 board put a Black OAC5 in position 1 and a IAC5 in position 2 on the board. The black wire and the red wire will go the the 1 and 2 position of the Black OAC5 and the Green and White wire will go to the 1 and 2 position of the IAC5.
When you then throw the light switch, power will be applied to the green wire. That will flow through the IAC5 turning on the LED in the module and flowing out through the white wire. Nothing happens......
You will need this computer interface board to make the magic happen... http://www.ebay.com/itm/Opto-2...
This one is for $199. I have found them as cheap as $35. Keep your eye out for them.
The software that you will write will constantly poll the input modules looking for input and then turn on the corresponding output module. The Black wire connected to the OAC5 is connected to the house current on the same circuit as the light bulb, so no overloading one circuit in your house to power all your lights.
OPTO 22 has a development kit for the PCI-AC5 found here... http://www.opto22.com/site/pr_...
It is FREE.
Turning on the OAC5 in software applies power to the red wire turning on the light bulb. The bad news is if your computer shuts down, then you can't turn on any of your lights. I have a patch panel that all my wires go to first, then I connect the G4PB24 with the input and output relays to the patch panel. That way if the computer ever does go down, I then jumper the green wire to the red wire and the light switch again works as normal.
Rinse and repeat for as many light fixtures that you have. You can use the OAC5 modules to switch anything in your home that runs off of house current. There are other modules that you can use with the board too. Once you have the basics down then start fooling with the others.
As for temperature readings Maxim has a 1 wire thermometer a DS18S20... http://www.maximintegrated.com....
They cost about 2 dollars each in small lots... You have to have a login ID to purchase them... https://memcenter.maximintegra... Registration is free.
You read them from a RS485 serial port. If you have had no problem pulling wire for the light switches, you can use the same wire for these. I use Black to the right leg, white to the center leg and the red wire to the left leg if you don't want to use the parasitic power mode. I've had one of these reading the outside temperature of my house since 1995. Source code to read them is posted on their website.
Send me an email for help with the software.