Smoke detectors are used as early warning systems for detecting smoke. Most smoke detectors have their own inbuilt pre-warning and if there is enough smoke detected, the main alarm system will be activated. If you are monitored, the monitoring centre receives a signal from your alarm and will act as per your monitoring instructions.
There are two types of smoke detectors: Battery backup and non-battery backup. Both are powered by the alarm system. Generally, non-battery backup smoke detectors are used in commercial properties.