Reactivating a fire alarm system refers to the process of restoring the system to full operational status after it has been deactivated or taken out of service for maintenance, repairs, or upgrades. The specific steps for reactivating a fire alarm system will depend on the type of system, but may include the following:

• Conducting a thorough inspection of the system's components, including smoke detectors, heat detectors, manual pull stations, horns, strobes, and control panels, to ensure that they are in good working condition and free of damage.
• Testing the system's sensors and alarms to ensure that they are functioning properly and are able to detect and respond to a fire.
• Conducting a full system functional test to confirm that all components of the system are working together correctly and that the system is able to provide the intended level of protection.
• Updating any necessary documentation, such as inspection and test records, to reflect the system's current status.
• Notifying any relevant authorities, such as the local fire department, that the system has been reactivated and is fully operational.

It's important to note that reactivating a fire alarm system should only be done by a qualified and trained professional. This includes a professional who has the knowledge of the local code, regulations and the fire alarm system.