An energy monitor is a simple device that you can fit it yourself. It works with your existing electricity meter to give you an indication of your electricity use. Energy monitors cannot communicate with your energy supplier and do not directly affect your bill.
Smart meters, on the other hand, are new meters that will replace existing gas and electricity meters and provide a communication channel between your home and your energy supplier. This means your energy supplier will have the ability to read your meter remotely and use this information to bill you for your actual energy use.
They come with a Smart energy display for you to place in your home, much like the energy monitor, that will show you how much gas and electricity you’re using and are automatically updated with your energy prices