System Sensor D4120 4-Wire Duct Smoke Detector

The System Sensor D4120 is a commercial 4-wire duct smoke detector designed for monitoring smoke within HVAC duct systems. As part of the InnovairFlex™ Series, it continuously samples air flowing through supply and return ducts to detect smoke before it is distributed throughout the building, helping initiate HVAC shutdown and other programmed fire alarm functions.

The detector features low-flow smoke detection technology, a plug-in smoke sensor, dual DPDT relay outputs, remote test capability, and a flexible housing that accommodates both square and rectangular mounting footprints. This product is intended exclusively for commercial fire alarm installations.

Product Functions

• Detects smoke within HVAC duct systems
• Monitors supply and return air ducts
• Initiates HVAC shutdown
• Provides alarm and supervisory outputs
• Supports remote testing and reset
• Supports interconnection for multiple air handlers
• Monitors detector cover tamper condition
• Continuous HVAC smoke monitoring

Electrical & System Information

The D4120 is a conventional 4-wire duct smoke detector that operates from 24 VAC/DC or 120 VAC power sources. It incorporates separate alarm, supervisory, and auxiliary relay outputs, allowing independent control of fire alarm systems, HVAC equipment, and building automation devices.

The detector operates in duct air velocities from 100 to 4,000 ft/min and supports local testing through a magnetic test switch or cover-mounted Test/Reset button. Remote testing is available using compatible RTS151, RTS151KEY, or RTS2-AOS remote test stations.

Features

• Commercial 4-wire duct smoke detector
• InnovairFlex™ low-flow technology
• Plug-in smoke sensor
• Dual DPDT Form-C relay outputs
• Alarm and supervisory contacts
• Remote test capability
• Test/Reset button
• Magnetic test switch
• Cover tamper monitoring
• Flexible square or rectangular mounting
• Interconnect capability for multiple air handlers
• Low-profile housing

Mounting & Design

The D4120 features a pivoting housing that installs on both square and rectangular ductwork, allowing installation flexibility while minimizing retrofit labor. Tool-free sampling tube installation from either side of the detector simplifies field installation.

The removable plug-in sensor head allows inspection, cleaning, testing, and replacement without removing the detector housing or disturbing field wiring. Compatible sampling tubes are selected according to duct width and are ordered separately.

Protection & Applications

Suitable for:

• HVAC Supply Ducts
• HVAC Return Ducts
• Air Handling Units
• Mechanical Rooms
• Office Buildings
• Hospitals
• Schools
• Warehouses
• Industrial Facilities

Compatibility

Compatible with:

• Conventional Fire Alarm Control Panels
• Building Automation Systems
• HVAC Shutdown Circuits
• RTS151 Remote Test Station
• RTS151KEY Remote Test Station
• RTS2-AOS Multi-Signaling Accessory
• RA100Z Remote Alarm LED
• APA151 Remote Annunciator
• D4S Replacement Sensor
• D4P120 Power Board
• InnovairFlex™ Sampling Tubes (DST Series)

Always verify compatibility with the installed fire alarm control panel, HVAC control equipment, power source, sampling tube length, and project requirements before installation.

Technical Specifications

Manufacturer: System Sensor

Parent Company: Honeywell

Model: D4120

Series: InnovairFlex™

Product Type: 4-Wire Duct Smoke Detector

Detection Method: Smoke Sensing Chamber

Power Supply: 24 VAC/DC or 120 VAC, 50/60 Hz

Relay Outputs: Two DPDT Form-C Auxiliary Relays

Air Velocity Range: 100–4,000 ft/min (0.5–20.3 m/s)

Operating Temperature: –4°F to 158°F (–20°C to 70°C)

Storage Temperature: –22°F to 158°F (–30°C to 70°C)

Operating Humidity: 0%–95% RH Non-Condensing

Reset Time: 0.6 Seconds Maximum

Power-Up Time: 35 Seconds Maximum

Test Methods: Cover Test/Reset Button, Magnetic Test, Remote Test Station

Cover Tamper Detection: Yes

Dimensions (Rectangular): 14.38 × 5.0 × 2.5 in. (365 × 127 × 64 mm)

Weight: 2.5 lb. (1.14 kg)

Application: Indoor Commercial HVAC and Fire Alarm Systems

Listings: UL 268A Listed for duct smoke detector applications. Verify product labeling and project requirements before installation.

Applications

The System Sensor D4120 is designed for commercial fire alarm systems requiring smoke detection within HVAC ductwork. Typical applications include office buildings, hospitals, schools, industrial facilities, warehouses, hotels, retail centers, mechanical rooms, and other commercial occupancies where early smoke detection and HVAC shutdown are required to limit smoke distribution through air handling systems.

D4120 Datasheet