Fire alarm notification appliances — the horns, strobes, and speaker-strobes that alert building occupants to evacuate — are a critical link in the fire alarm chain. Despite their importance, they’re often overlooked during preventive maintenance until they fail a test or visibly malfunction. Understanding the different types of notification appliances, the code requirements that govern their selection, and when replacement is warranted will help facilities managers and fire alarm technicians make better decisions about this essential system component.
The Four Main Types of Notification Appliances
Horns (Audible-Only) — Produce an audible alarm tone without a visible strobe. Horns alone are generally not sufficient for new commercial installations, as ADA requirements mandate visible notification in most spaces. However, they remain in service in many older buildings and are still used in specific applications like mechanical rooms where visual notification isn’t required.
Strobes (Visual-Only) — Produce high-intensity white light flashes at a regulated rate (1-2 flashes per second). Required by ADA in areas where audible notification would be impractical or inaccessible to individuals with hearing impairments — restrooms, sleeping areas in hotels, and other spaces where sound attenuation is significant.
Horn-Strobes (Combination) — The most common notification appliance in modern commercial buildings. Combines audible horn and visible strobe in a single unit. Horn-strobes simplify installation (one device instead of two) and reduce wiring complexity. The Simplex Multi-Candela Horn-Strobe is a widely used combination appliance with selectable candela output — a key feature for meeting ADA requirements.
Speaker-Strobes — Combine a visible strobe with an audio speaker capable of reproducing voice messages. Used in systems with mass notification or voice evacuation capabilities (required in high-rise buildings, assembly occupancies, and others under IBC and NFPA 72). Speaker-strobes are wired differently than horn-strobes — they connect to amplified audio circuits rather than standard NAC circuits.
NFPA 72 and ADA Candela Requirements
NFPA 72 specifies minimum candela (light output) requirements for strobes based on room size and strobe placement. The standard defines required candela levels for wall-mounted strobes at different room dimensions, and requires that strobes be visible from any point in the protected space. For large open spaces, high-candela strobes or multiple strobe units are required to achieve coverage.
ADA Standards for Accessible Design (28 CFR Part 36) require visual notification in “common use areas” and areas open to the public, and specifies a minimum of 75 candela for wall-mounted strobes in most applications. Key requirements include:
- Strobes must be mounted at 80″ above the floor or 6″ below the ceiling, whichever is lower
- A single strobe must be visible from any point in the protected space
- Multiple strobes in the same space must flash synchronously (within 10ms of each other) to prevent seizure risk for photosensitive individuals
Synchronization is achieved either through synchronized NAC power supplies or through appliances with built-in synchronization protocols (such as the Wheelock SYNC protocol or System Sensor COSYNC). When replacing notification appliances, verifying compatibility with the existing synchronization protocol is essential.
When Notification Appliances Need Replacement
Several conditions trigger notification appliance replacement in commercial buildings:
Corrosion and physical damage — Notification appliances in high-humidity environments (stairwells, parking garages, exterior locations) are prone to corrosion of the housing and internal components. Corroded horn-strobes may produce degraded tone output or fail entirely during testing.
Failed function testing — NFPA 72 requires annual function testing of all notification appliances. Any appliance that fails to activate, produces diminished output, or fails synchronization testing must be replaced.
Code upgrade requirements — Buildings undergoing renovation or change-of-use may trigger a requirement to upgrade notification appliances to current ADA candela requirements. If your existing appliances are 15-candela units but the current code requires 75 candela for the space, replacement is mandatory upon renovation permit.
Discontinued appliance models — When a specific notification appliance model is discontinued, spares become harder to source and maintaining visual consistency throughout a building becomes challenging. Planning a phased replacement program while the preferred replacement model is available simplifies future maintenance.
Simplex and Wheelock Product Lines
Two of the most widely installed notification appliance product lines in commercial buildings are Simplex and Wheelock (now part of Eaton). Simplex notification appliances are designed for use with Simplex panels and NAC circuits, with synchronized operation via Simplex’s MAPNET protocol in some configurations. The Simplex notification appliance catalog includes horn-strobes and strobes in multiple candela ratings.
Wheelock appliances — branded as Eaton/Wheelock — are among the most widely distributed in the industry and are compatible with most NAC circuits regardless of panel manufacturer, making them a common choice for replacement and renovation projects. System Sensor is another major supplier with broad compatibility. Browse the System Sensor product line for notification appliance options.
Selecting the Right Replacement Appliance
When selecting a replacement notification appliance, verify:
- Candela rating — Must meet or exceed the requirement for the space per NFPA 72 Table 18.5.4.3.1
- Synchronization protocol compatibility — Must match the existing NAC power supply or panel NAC output synchronization protocol
- Voltage range — Standard NAC circuits operate at 12VDC or 24VDC; verify the appliance voltage range matches the circuit
- Mounting pattern — Back-box mounting must match the existing installation (standard 4″ square or 2-gang)
- UL listing — Only UL-listed appliances should be used in life safety applications
