Smoke detectors are arguably the most important component in any security system and are simply hardwired or wireless sensors that detect the presence of visible or invisible particles produced by combustion, smoke and fire. They are available in Therma models that require the presence of both smoke and a rate of rise in room temperature and in models with their own sounders. Therma models are desirable when a smoke condition may be present without fire, (such as bacon burning in a kitchen). This prevents false alarms when only smoke is present. In areas where smoke is likely to be present without fire, a heat detector is desirable.
If your security system doesnt include at least one smoke detector tied into the security system, a fire condition will not trigger an exterior siren or a call to a central monitoring station. If your family is overcome by fumes and cannot escape or call the fire department, your inexpensive hardware store model will not be loud enough to alert your neighbors. Who is going to call the fire department for your family?