we leave all sorts of electrical devices on, or in idle mode all the time(don't forget to turn those computers, power supplies and battery chargers off) if you are really anal about it, you should go down stairs and turn off the main power supply.....and while you're at it, shut off the water inlet to the house.

we do have a voltage monitor on our household voltage. about 5 years ago, the neutral on the power input to our house was severed. in house voltage got close to 200. the computer power protectors issued no warnings.