Access control a is way of limiting access to a system or to physical or virtual resources. In computing, access control is a process by which users are granted access and certain privileges to systems, resources or information.In access control systems, users must present credentials before they can be granted access. In physical systems, these credentials may come in many forms, but credentials that can’t be transferred provide the most security.

A fire alarm is an electronic device made to produce audible/visual warning to residents if a fire is present. Most fire alarm systems are activated by smoke detectors, heat detectors, or fire alarm pull stations. A common misconception is that a “three-alarm fire,” for example, means that three firehouses responded to the fire.

This is not the rule behind the naming convention, albeit some cities may use the number of firehouses responding for multi-alarm designations because that is the simplest way to determine an alarm number. The most widely used formula for multi-alarm designation is based on the number of units (firetrucks for example) and firefightersresponding to a fire; the more vehicles and firefighters responding, the higher the alarm designation. (Note: In most cities, a “unit” can be anything from a tanker or ladder truck to rescue vehicles to even cars driven by the chief and deputies.)

With this unit/firefighter alarm designation, the initial dispatch is referred to as a “first alarm” and is typically the largest. Subsequent alarms are calls for additional units, usually because the fire has grown and additional resources are needed to combat it, or that the incident is persisting long enough that firefighters on scene need to be replaced due to exhaustion.

Requests for units and firefighters from outside jurisdictions do not normally occur in multi-firehouse urban areas until elevated alarms are reached (alarm three and above), but will depending on the location of the incident and the condition of the authority having jurisdiction at the time of the incident.