What defines a stand-alone fire alarm?

A stand-alone fire alarm is defined by its ability to operate independently without the need for a central control panel. This means that it functions as a self-contained unit that detects fire or smoke and signals an alarm on its own, without relying on interconnected systems or external monitoring. Stand-alone alarms are often used in residential settings and are a straightforward solution for providing fire detection in individual areas.

The features associated with the other choices highlight characteristics typically found in more complex fire alarm systems. For instance, interconnected alarms can communicate with each other, alerting all units in a building when one detects a fire, which emphasizes the collaborative nature of those systems over the autonomy of a stand-alone alarm. Similarly, while many alarms can trigger when smoke is detected, a stand-alone fire alarm may also respond to heat or carbon monoxide, depending on its design. Finally, the option of automatically contacting the fire department describes a feature more commonly found in monitored systems rather than independent units, which don't have the capability to establish external communications independently. Thus, the defining trait of a stand-alone fire alarm is its operation without reliance on a control panel or other systems.