Check to make sure the system is powered up. Press any button on the alarm panel; if it lights up, the panel is still plugged in. If not, look in the basement or one of your crawlspaces for a black box. Open the box and plug in the system.
Contact the former owners or the realtor and ask for the alarm code. If necessary, contact the manufacturer of the alarm panel and contact the company directly for instructions on how to clear and enter new codes into the system. You must have a valid pass code to use an existing system.
Input the pass code (typically a four-digit number) and press “Arm” or “Stay” on the panel. This will arm the system. Open a door equipped with a sensor, and the alarm should sound. Deactivate the alarm by entering your code again (after you shut all doors and windows equipped with sensors).
Contact a monitoring company to start formal alarm services. You can use your alarm on your own but only you and your neighbors will hear it if it goes off. If you hire a commercial company, the company will monitor your alarm and notify the authorities if needed.