The far left hand button is the power button. While the DSM250 is off, press the power button once to turn the DSM250 on. While the DSM250 is starting up, you will see a screen indicating that the DSM250 is booting up. Once the DSM250 has initialized, you will see the opening splash screen where you will need to acknowledge the legal disclaimer by pressing the Accept button. With the DSM250 turned on, if you press and hold the power button, a countdown screen appears where you need to continue to hold down the power button. If the power button is released before counting down to zero, then the DSM250 will not turn off. This is done so that an accidental press of the power button does not immediately shut down the DSM250. If you hold down the power button for a full three seconds, then the DSM250 will shut down. The power button is also used to acknowledge an alert. For example, if an alert is sounding, a quick press of the power button will acknowledge the alert which will stop the flashing and enunciators from sounding.