Set the alarm to go on and off with certain passwords, which will most likely be numerical -- depending on what alarm system is installed.
Enter the code on the keypad before you leave the house, to arm the automated alarm system. Most alarm systems allow 30 seconds to exit the home, before arming.
Enter the home again; the alarm will usually beep for a set amount of time, which allows the correct code to be entered. Once disarmed, the alarm is in standby, until a new authorization is given.