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A weak factory horn can be hard to hear in busy traffic, but a louder replacement is only useful if your vehicle can support it. The HELLA B133 SuperTone Horn Set (3AG 003 399-801) combines 300 Hz and 500 Hz tones with a manufacturer-rated 118 dB(A) sound level at 2 meters. Each 123 mm disc horn draws up to 5.5 A, so the pair needs more space and electrical planning than many stock replacements. This specifications-based review explains the sound, fit, wiring demands, and package details you should check before buying.
Quick Verdict
Editorial Rating: 8.5/10 (based on published specifications and installation tradeoffs, not hands-on testing)
Best For: Drivers with a 12 V vehicle who want a loud, dual-tone warning horn and have enough mounting space and electrical capacity.
Bottom Line: The 118 dB(A) rating, 300/500 Hz pairing, and IP65-rated construction make this a strong warning-horn upgrade. However, its two large housings and combined electrical demand make fitment and correct wiring essential.
Key Takeaways
- The HELLA B133 combines a 300 Hz low tone and 500 Hz high tone to create a distinct dual-tone warning signal.
- HELLA specifies 118 dB(A) at 2 meters (with a ±3 dB tolerance in its technical brief). Different testing distances make direct comparisons with other brands unreliable.
- Each horn measures about 123 mm in diameter, with a listed overall height of 135 mm, width of 125 mm, and depth of 85 mm.
- The 12 V pair is rated at 66 W and up to 5.5 A per horn, or 132 W and up to 11 A when both operate together.
- Each horn uses 6.3 mm flat-blade contacts; a suitable horn relay, correctly sized protection, and a secure mounting point may be needed.
- HELLA lists IP65 protection, ECE R28 approval, and an operating range from -40 °C to +60 °C.
- Check relay inclusion with the seller. HELLA currently lists 3AG 003 399-821 as the 5-pin-relay version, but another HELLA brief describes the -801 kit as including a relay.
Key Features and Specifications
| Specification | Detail |
|---|---|
| Brand | HELLA |
| Product | B133 SuperTone Horn Set |
| Part number | 3AG 003 399-801 |
| Product type | Electric dual-tone disc horn set |
| Rated voltage | 12 V |
| Low tone | 300 Hz |
| High tone | 500 Hz |
| Sound level | 118 dB(A) nominal, measured at 2 m; ±3 dB manufacturer tolerance |
| Power consumption | 66 W per horn |
| Maximum current | 5.5 A per horn (up to 11 A for two horns) |
| Combined rated power | 132 W (2 × 66 W) |
| Diameter | 123 mm |
| Overall height | 135 mm |
| Width | 125 mm |
| Depth | 85 mm |
| Connection | Open 6.3 mm flat-blade contacts |
| Mounting | Metal bracket for M8 fixing screw, as specified in HELLA documentation |
| Housing | Black metal housing with red protective grille |
| Quantity | 2 horns, one low tone and one high tone |
| Relay/package note | Confirm contents for -801; HELLA also lists -821 as a package with a 5-pin relay |
| Protection | IP65 |
| Approval | ECE approved, fulfils ECE R28 |
| Temperature range | -40 °C to +60 °C |
| Specified service life | 100,000 cycles under ECE R28 testing; not a warranty period |
| Typical application | 12 V cars, utility vehicles, and off-road use with verified fit and wiring |
What Is the HELLA B133 SuperTone Horn Set?
The B133 is a two-piece electric disc-horn set. One horn produces the 300 Hz low note, while the other produces the 500 Hz high note. Both sound together through the vehicle’s horn switch and appropriate control circuit, producing a fuller warning tone than a single-frequency unit.
HELLA promotes this set for cars and demanding uses, including off-road driving. It is best suited to buyers who can house two 123 mm units and support their combined current draw. It is not a universal plug-and-play solution.
How this review was assessed: The specifications and comparisons were checked against HELLA’s published product information and its B133 technical documentation. The 8.5/10 score is an editorial assessment of the listed features and fit requirements. We did not conduct a hands-on sound or installation test.
Who Should Buy It?
Best For
- Drivers seeking HELLA’s 118 dB(A) dual-tone warning signal in a 12 V vehicle.
- Vehicles with enough front-end space for two 123 mm disc horns.
- Owners able to check a two-horn circuit that can draw up to 11 A, or hire an installer.
Skip If
- Your vehicle has very limited space behind the grille or bumper.
- You need a direct plug-in horn with no wiring or mounting changes.
- Your vehicle does not use a 12 V electrical system.
Design and Build Quality
The B133 uses a black metal body with a red protective grille. Each disc measures 123 mm across, with an overall listed height of 135 mm, width of 125 mm, and depth of 85 mm. That can crowd a tight grille cavity, especially when the mounting brackets and terminals need extra clearance.
HELLA specifies IP65 protection and an operating range of -40 °C to +60 °C. The housing is designed to resist dust and water jets, but IP65 does not mean it can be submerged. Keep the blade terminals away from pooled water, and make sure the body and bracket cannot rub against other components.
Performance and Sound Quality
The main attraction is the 118 dB(A) rated output at a 2-meter test distance. HELLA’s technical brief states a ±3 dB tolerance. The 300 Hz note contributes a lower pitch, while the 500 Hz note adds a higher pitch, so the pair sounds more layered than a single-tone horn.
The high and low frequencies are intended to make the warning signal more noticeable in road noise. A rated sound level is not a guarantee that every driver will hear it through a closed cabin, loud music, or heavy traffic. Use the horn for brief warnings, not prolonged sounding.
Placement matters as much as the listed sound level. A rigid metal bracket helps keep the horn steady. Avoid blocking the grille with thick trim, pressing the housing against the radiator support, or placing the terminals where road spray can pool.
Fit, Compatibility, and Installation
The B133 is a universal-style 12 V set, not a vehicle-specific connector kit. Check the mounting cavity against the 123 mm diameter and the 135 × 125 × 85 mm listed dimensions. Leave room for the bracket, terminals, wires, and airflow around nearby cooling components.
Electrical load is the second major fit issue. Each horn is rated at 66 W and up to 5.5 A. Together, that is 132 W and up to 11 A at the specified rating. Do not assume the original horn circuit or steering-wheel control wiring can supply this load directly.
The B133 uses open 6.3 mm blade terminals. Depending on the vehicle, installation may require a suitable relay, fuse, wire gauge, connectors, and brackets. Match those parts to the car’s wiring diagram and HELLA’s instructions. If you cannot confirm the circuit rating or relay setup, use a qualified automotive electrician.
Before You Buy: Check the exact kit contents, not just the part number. HELLA’s current catalog identifies 3AG 003 399-821 as including a 5-pin relay, but a separate HELLA 2025 brief describes 3AG 003 399-801 as a kit with a relay. Ask the seller to confirm whether the -801 box you will receive includes the relay, mounting hardware, and wiring items you need.
How It Performs in Real Use
For Daily City Driving
In stop-and-go traffic, the 300/500 Hz pairing is designed to create a clear warning signal when engines and street noise compete for attention. That benefit depends on correct mounting and power delivery; the 118 dB(A) figure is a laboratory rating, not a measurement inside traffic.
For Highway Driving
Wind and tire noise can make a weak horn harder to notice at speed. HELLA describes the B133 as a strong-output warning horn, but its rating does not tell you how far away another driver will hear it. Use it only when a warning is needed and local law permits.
For Off-Road and Utility Use
The red grille and metal housing suit rugged mounting locations, while IP65 protection helps against dust and splashing water. Avoid submerging the unit or letting mud build up in front of it. Inspect wiring after rough-road use because vibration and debris still affect exposed components.
For Long-Term Ownership
HELLA specifies 100,000 cycles under its ECE R28 test conditions. That is a test benchmark, not a promise of years in service. Check the mounting points and electrical contacts during routine vehicle inspections, especially after winter roads or off-road trips.
Installation Tips for Better Results
- Measure first: Confirm that both 123 mm horns can fit without touching the radiator, fan, bumper, grille, or other moving parts.
- Use a rigid mounting location: A solid bracket reduces vibration and helps keep each horn correctly positioned.
- Plan for the electrical load: Do not assume the original factory horn wiring can safely handle the pair without checking the circuit.
- Protect the connections: Use suitable automotive connectors and keep terminals away from locations where water can pool.
- Verify part number and package contents: The 3AG 003 399-801 and relay-equipped 3AG 003 399-821 are not the same package.
- Test before final assembly: Confirm both the 300 Hz and 500 Hz units operate before reinstalling trim or bumper components.
Pro Tip: Before removing the factory horn, trace its connector and check whether it uses a relay. Measure with the grille or bumper refitted in mind; the 123 mm disc diameter does not include needed wiring and bracket clearance.
Compatibility and Safety
The B133 is designed for a 12 V vehicle, but a matching battery voltage is only the first check. The original horn fuse, wiring, relay, switch circuit, and mounting location must be able to support the two-horn setup. Do not increase a fuse rating just to stop nuisance blowing without checking the entire circuit.
HELLA lists ECE R28 approval, which covers the horn as a type-approved warning device. It does not guarantee that every installation or use complies with local rules. Check any vehicle inspection and noise requirements that apply to you.
Poor connections or under-sized wiring can cause voltage drop, intermittent operation, blown fuses, or overheating. Protect wires from sharp edges and moving fans. Test with brief horn presses in a safe place, with people away from the front of the vehicle; the rated sound is very loud at close range.
Pros and Cons
Pros
- 118 dB(A) nominal sound-pressure rating at 2 meters.
- 300 Hz and 500 Hz dual-tone design creates a distinctive warning signal.
- IP65-rated body resists dust and water jets when correctly installed.
- ECE R28 type approval and 100,000-cycle test specification.
- Metal housing and protective grille are designed for demanding vehicle use.
Cons
- The 123 mm housings may be too large for tight factory horn locations.
- Combined demand reaches 132 W and up to 11 A, requiring circuit checks.
- Relay inclusion is unclear across HELLA materials; seller confirmation is needed.
Is It Worth the Price?
The B133 is worth considering when you value a distinctive, high-output two-tone warning over the simplest swap. Its nominal 118 dB(A) rating, 300/500 Hz tones, IP65 rating, and ECE R28 approval make the specification case. Actual value depends on the current selling price, which was not confirmed for this review.
The tradeoff is the full installed cost, not just the horn price. You may need a relay, suitable wiring, fuse protection, and custom placement. If your vehicle has little space or a low-capacity horn circuit, a compact replacement may offer better overall value.
How It Compares to Alternatives
HELLA’s M26 Sharp Tone set is a smaller option for tight spaces. Its published 115 dB(A), 350/415 Hz, and 42 W specifications place it below the B133’s nominal sound output and power draw. Check the exact M26 variant and dimensions before choosing it for a particular vehicle.
The HELLA B36 uses 335/400 Hz tones and is rated around 116 dB(A), providing another sound character to compare. These are manufacturer figures, not results of a matched side-by-side test. Choose the B133 for its 300/500 Hz pairing if space and wiring allow.
Frequently Asked Questions
Is a relay included with the HELLA B133 3AG 003 399-801?
It is not safe to assume either way. HELLA’s current catalog names the -821 kit as including a 5-pin relay, but a separate 2025 HELLA brief describes the -801 set as including a relay. Check the seller’s exact box contents before ordering extra parts.
Does the B133 include a mounting bracket?
HELLA describes an M8 mounting bracket for this horn family. However, do not assume the seller supplies every mounting fastener or adapter your vehicle needs. Check the listing and compare the bracket with your mounting point.
Will the HELLA B133 fit any 12 V car?
No. Your vehicle needs space for two 123 mm horns, suitable mounting hardware, and a circuit designed for up to 11 A combined rated demand. Confirm fuse and relay capacity before choosing a universal set.
What frequencies does the B133 use?
One disc is tuned to 300 Hz and the other to 500 Hz. The two sounds operate together when installed as a pair. Replacing only one disc changes the intended sound.
How loud is the HELLA B133?
HELLA rates it at 118 dB(A) at 2 meters, with a ±3 dB tolerance in its technical brief. You should only compare that number with other horns tested at a similar distance and by a similar method.
Can the B133 be installed on a motorcycle?
The B133 requires 12 V power, but it is not a motorcycle-specific kit. Two 123 mm discs and their combined current draw can be difficult to accommodate. Check your charging capacity, fit, and local horn rules first.
What is the warranty period?
No fixed warranty term for this exact Amazon listing was verified. Confirm whether coverage comes from HELLA or the seller and keep your purchase record. The 100,000-cycle test specification is not a warranty.
Does the B133 need regular maintenance?
No routine servicing schedule was verified for this set. Periodically check for loose bolts, corrosion at the 6.3 mm contacts, damaged wiring, or blocked grilles. Replace damaged parts rather than forcing a malfunctioning horn to work.
The Bottom Line
The HELLA B133 SuperTone Horn Set earns its 8.5/10 editorial rating for a strong nominal 118 dB(A) output, distinct 300/500 Hz sound, and IP65 protection. Buy it if your 12 V vehicle has room for both 123 mm discs and an appropriate electrical circuit. Skip it if you need a small direct-plug replacement or cannot verify the installation requirements.
