Check the office to make sure that all the employees are out of the building. If an employee is still roaming around and the alarm is armed it will sound and can lead to a ticket for a false alarm.
Punch in the arming code into the keypad. The system will activate only if the proper code is entered. Some systems will display the code. Push the enter button or the button that says armed.
Walk to the door and leave the building. Lock the door from the outside. Most alarms give you one minute to exit after entering the arming code.