-For a central controller, I use the Universal Devices ISY-994i. This provides a web-interface for status, and quick toggle-controls, but it's also where I do my "programming"
-if you buy and install an Insteon switch, it will "just work" as a regular switch - others in your home will have zero learning-curve.
-they do have some universal I/O modules with dry contacts, etc. You may be able to work with these to perform your temperature monitoring and control, along with water-level detection, etc. See if it would work for you.
And, here is a bit more "geek" for you to ponder:
The Insteon signalling uses both a data-burst on the AC power-line, and also a radio-frequency data burst. Each device will repeat a burst (up to 3 hops only, or something like that) - in practise, I've found it really, really reliable. I started with just a controller and a couple of (AC-powerline-only) switches, but this required me to add a hardware phase-bridge, so data-bursts on one phase of my house-wiring could reach devices on the other phase. As I added more devices, especially more wireless devices, the mesh got better and better.
The Insteon switches will require 3 wires in your switch-box:
1) Hot wire. The Insteon switch will use a bit of power, as well this is what powers your light or other device(s). Typically it's a black wire.
2) Load wire. This is what goes to your devices.
3) Neutral wire. Typically this is white, and can sometimes be a problem. My older (1950's) home had all the hot-and-neutral wires run to the lights first, then a pair of wires ran down to the switches... this won't work
Each Insteon switch is internally pretty cool: it's comprised of two parts:
1) a switch part, that detects when you press the switch, and reports this data-event
2) a responder part, which receives a data-event and closes the circuit (with relay, or whatever).
So, you can actually have a single switch act to control several devices, if you want
The "programming" is not really very geeky: it's more just a set of conditions and actions, selected from drop-down dialogue boxes. That said, you can do some fun stuff, like:
- change actions based on sunrise-sunset times (great for lighting)
- use a motion-detector, which also contains an ambient-light sensor! I use one of these outside, to tailor my lighting to the Pacific Northwest's gray and dreary winter days.