For many of us, the computer has become an essential part of our work life, both at the office and at home. When you're not on your laptop or desktop, it often goes into something called "sleep mode" to conserve energy, but it can be "woken up" with the stroke of a key. If you want to save energy when using your computer, you should turn off the monitor on your desktop if you aren't going to use it for more than 20 minutes. If you plan to not use your computer for more than two hours, you should shut down the whole system completely. Even though there is a small amount of energy used to turn on a computer, it's not as wasteful as having it in sleep mode for long periods of time.