Types of Home Fire Alarm Systems
Published: 09/30/2009 by Home Alarm Directory
Home fire alarm systems come in two main categories: self-contained units and building-wide systems. Self-contained units are the everyday smoke detectors people have in their homes. They're either powered by batteries or hooked into the house's electrical system. This single-station unit sounds an alarm out of the fixture itself when its internal sensors detect smoke.
Building-wide systems are integrated alarms that all sound when a single sensor detects smoke or when the alarm is manually triggered, like when people pull a fire alarm. These systems may be wired or wireless. Either way, detectors are linked to a control panel that can provide backup power in the case of a power failure and can summon the Fire Department whether anyone is home or not.
Types of Detectors
There are two primary detectors available for use in a home fire alarm system: smoke or heat detectors. The choice depends on several variables: sensitivity, speed, accuracy, conditions of detector locations, whether detectors will be integrated into a controlling system, and code requirements.
Smoke Detectors
Smoke detectors can be used in either type of home fire alarm system. If one has ever set off a smoke detector from a cooking mishap, it's very apparent how sensitive they are. They sound an alarm when they pick up even a tiny amount of smoke. Self-contained units run on a 9-volt battery or the 120-volt house current. Some of the latter units will switch to a backup battery in the event of a power failure. Building-wide system units get power from a central source. They connect to the control panel to signal the alarm.
A home fire alarm system uses two types of smoke detectors: photoelectric and ionization. Photoelectric detectors rely on the way light bounces off smoke to detect a fire. Inside the unit's smoke-sensing chamber, light projects onto a black background. If enough smoke filters in, this light will be reflected, hitting a sensor that triggers the alarm. These types of detectors are best at detecting heavy-smoke fires. Ionization detectors use tiny amounts of radiation to detect smoke. Inside the unit's smoke chamber, a small electrical current flows from one point to another. When smoke enters the chamber, the current is disrupted and the alarm sounds.
Heat Detectors
A home fire alarm system might also use heat detectors, which sound when the temperature in the area around the detector rises to a certain level. Because heat detectors are blind to smoke, some studies suggest that they may not offer an early enough warning for people to escape if they're used alone. They can be helpful in kitchens and attics where smoke detectors normally cannot be placed, but they're not advised for bedrooms. Types include: fixed-temperature, rate-of-rise, and combined.
Fixed-temperature heat detectors sound when the temperature hits a certain predetermined level. Some units have a non-restorable detector, meaning once the alarm sounds, the detector must be replaced.
Rate-of-rise detectors measure the rate of change of temperature. If the temperature rises faster than its set level, the alarm will sound. These units are usually self-restoring. Some units utilize both these technologies to warn at both a fixed temperature and a quickly rising temperature.
Given these many options, an effectively-designed home fire alarm system will warn occupants early, allowing them the chance to escape should the worst happen.
