I work for Generac in the Whitewater, WI plant and Im a tester, (when the generator reaches the end of the assembley line its my job to hook it up, run it, make sure that it works right and fix it if it doesnt) so I work with these units every day and pretty much know them inside and out.
They run on either natural gas or LP and are completely self-contained and do everything on their own. They will do their job and keep the power on whether you are home or not.
What they do is that they sense when the power goes out and then after 10 seconds of sensing utility power loss, the generator starts and there is a transfer switch that switched your home back and forth between running on utilty power and power from the generator. The generator then runs and senses when the utility power comes back on. After it senses utility power for 10 seconds, the transfer switch switches back to running your home on utility power and the generator then goes into a cooldown mode where it runs for 75 seconds and then shuts off.
All in all, they are pretty good units and the vast majority of them pass through test the first time and run perfectly.
Home standby units come in sizes of 8KW, 10KW, 12 KW, 14KW, 16KW, 17KW and 20KW.
The engines as pretty fancy too. On the 10kw and bigger units they have electronically-controlled stepper motor governors, high temp shut, low oil shutoff, overspeed shutoff, underspeed shutoff. In the case of the 8kw units, they have all the features of the bigger motors, but they have a mecanical governor.
All in all, a great product that is made in America by an American company.