A fire alarm is a unit made of several devices, which uses visual and audio signalization to warn people about a possible fire, smoke, or carbon monoxide occurrence in the area of coverage. Fire alarms are usually set-in fire alarm systems to provide zonal coverage for residences and commercial buildings. The warning signal is either a loud siren/bell or a flashing light, or it can include both. Some fire alarm systems use additional warnings, such as sending a voice message or making a phone call.