For what you are describing this would probably be the easiest place to start:

http://www.amazon.com/Arduino-Cookbook-Michael-Margolis/dp/1449313876/ref=sr_1_1?ie=UTF8&qid=1405991223&sr=8-1&keywords=arduino+cookbook

as for the input to the microcontroller you can solder a wire to one side of the speaker in the smoke detector (assuming it is voltage compatible with the microcontroller you use).

Control should be done with an ssr, or using a triac would be good experience (these can be used in dc circuits too).

The only tools you should need are a multimeter, wire strippers, and side-cutters.

There are a number of tutorials out there Schmartboards feed on Facebook is good about listing them as well as free online books and such.

http://www.efytimes.com/e1/132790/Super-Useful-Tutorials-To-Learn-Various-Electronics-Concepts

When playing with ac always assume it is a live circuit until you have verified, and there can be more than one circuit in a box, check all of them. Never assume that the people who wired something knew what they were doing, you can find out the hard way they didn't, avoid supporting your self against something (especially metal when working near electric lines) I have been electrocuted while repairing the copper lines under a sink because the insulation was scraped off when the romex was run for the dishwasher (not my doing).

Now if I havn't scared you, have fun. It is ok to weld with a screwdriver every now and then.