Smart devices are things that connect to the internet.  Perhaps your fridge connects to the net to remind you to buy milk or to suggest possible recipes from the contents of your fridge.  Now there's even a smart mattress cover being designed.  Available soon, it will have many functions.  For example, it'll be able to connect to your thermostat to adjust your home's temperature after you fall asleep.  It could also be programmed to make sure your front door is locked and to start the coffee maker when you wake up.