- +Genuine HornBlasters three-bell metal horn, two inches shorter and about four pounds lighter than the full-size Outlaw
- +Honest spec sheet — HornBlasters publishes no dB number rather than inventing one
- +127H variant is sealed against the elements on both horn and air system, so it can live under the vehicle
- +Complete kit: pre-installed 1/4-in. electric valve, three wire runs, fuse kit, air line cutter, hardware and earplugs
- +Owner feedback on hornblasters.com averages 5.0/5 across 41 reviews at review time
- +2-year manufacturer's defect warranty on the kit
- −No published dB rating, test distance or chord frequencies, so loudness can't be compared on paper
- −~35-second recovery after a 4-5 second honk (2-3 seconds on the M3) — a burst horn, not a sustained one
- −M3 variant's tank-mounted compressor must be mounted upright in a dry enclosed spot or the warranty is void
- −Detaching the compressor from the tank voids the warranty on either variant
- −1/4-in. valve and air line limit airflow versus the 1/2-in. inlet on the full-size Outlaw
- −Returns can carry a 15% restocking fee; 25% compressor duty cycle rules out air-tool use
Methodology
This review aggregates publicly available information from manufacturer specifications, retailer listings, and verified user reviews. We do not perform hands-on testing. Last reviewed: September 13, 2026. Primary source: the official HornBlasters Mini Outlaw Train Horn Kit product page (which covers both the 3-liter M3 and the weather-resistant 127H variants), plus HornBlasters’ separate single-variant listings, the standalone Mini Outlaw horn page, and the KT Performance retailer listing for a price cross-check. Every number below comes from those pages; all URLs are in the Sources section at the end.
Quick verdict
The Mini Outlaw is HornBlasters’ shrunken take on its best-known three-bell horn, sold as a complete kit with either a compact 3-liter M3 air source ($369.99) or a weather-resistant 1.5-gallon 127H air system ($399.99). Both prices are listed against a $539.99 compare-at price on the combined kit page. It keeps the three-metal-bell format of the full-size Outlaw but trims two inches off the length and about four pounds off the horn, and it runs on a 1/4-inch air line so the whole system fits in tighter spaces. We rate it 4.2/5: the value, the honest spec sheet, and the perfect owner rating on HornBlasters’ own site earn real points, while the absence of any published decibel figure, the short honk-to-recovery ratio, and the M3 variant’s strict mounting rules keep it below the top tier. Our recommendation is the 127H weather-resistant kit, and that is the variant this review pins throughout.
What it is
The Mini Outlaw is a 3-chime metal train horn, which HornBlasters describes as “the same commanding presence, the iconic auditory experience, all wrapped up in a compact form factor” compared to the original Outlaw. The horn itself is sold standalone as the AH-MC3 (chrome) or AH-MC3B (Stealth Black) for $219.99. The kit reviewed here bundles that horn with a 12-volt on-board air system, a pre-installed electric valve, wiring, and hardware so that a first-time installer has everything except tools.
HornBlasters pitches it at drivers “where space is a premium but compromising on the authentic train horn tone is not an option.” In practice that means mid-size trucks, SUVs, Jeeps, and cars where an 18.5-inch full-size Outlaw will not fit. The kit page lists four SKUs: HK-MC3B-M3 and HK-MC3-M3 (3-liter, black or chrome) and HK-MC3B-127H and HK-MC3-127H (1.5-gallon weather-resistant, black or chrome). All four showed as in stock on hornblasters.com at review time. For the whole HornBlasters range, see our HornBlasters brand hub.
Specifications
All values are from HornBlasters’ product pages. The 127H column is the variant we recommend; M3 values are shown where they differ.
| Spec | Mini Outlaw 127H kit (M3 where different) |
|---|---|
| Part numbers | HK-MC3-127H chrome / HK-MC3B-127H black (M3: HK-MC3-M3 / HK-MC3B-M3) |
| Horn type | 3-chime metal train horn, 3 metal bells on a common manifold |
| Sound output | Not published by HornBlasters (no dB figure, no test distance, no chord frequencies) |
| Operating pressure | 120 PSI |
| Restart pressure | 90 PSI |
| Voltage | 12-volt DC |
| Max amp draw | 18 amps |
| Compressor | 2-liter air compressor, 25% max duty cycle at 100 PSI (M3: tank-mounted 3-liter compressor and tank combo) |
| Air tank | 1.5-gallon (6.6 L) 4-port tank (M3: 3-liter tank) |
| Honk time | 4-5 seconds (M3: 2-3 seconds) |
| Recovery, 90 to 120 PSI | 35 seconds (± 5 sec.) at 13.8 V |
| Full fill, 0 to 120 PSI | 2 min. 10 sec. (± 10 sec.) at 13.8 V (M3: 2 min. ± 10 sec.) |
| Horn dimensions | 16.5 in. L x 14.5 in. W x 11 in. H (419.1 x 368.3 x 279.4 mm) |
| Horn weight | 10.9 lb (4.95 kg) |
| Air source dimensions | 15.2 in. L x 5.9 in. W x 12.8 in. H (M3: 16.535 x 4.921 x 7.086 in.) |
| Air source weight | 13.75 lb (6.24 kg) (M3: not disclosed) |
| Valve | Pre-installed 1/4-in. electric air valve |
| Air line | 20 ft of 1/4-in. line (M3: 12 ft) |
| Drain port | 1/8-in. NPT (listed for M3) |
| Weather resistance | Horn and air system sealed against the elements (M3: must be mounted upright, enclosed, away from moisture) |
| Finish options | Stealth Black or Chrome |
| Price | $399.99 (M3: $369.99); compare-at $539.99 on the combined kit page |
| Shipping weight (retailer) | 38 lb per KT Performance |
| Warranty | 2-year manufacturer’s defect warranty; 30-day satisfaction guarantee |
One inconsistency worth flagging: the M3 variant’s marketing copy calls it a “110 PSI air system,” but the spec table on the same page lists 120 PSI operating and 90 PSI restart for both variants. We have used the spec-table figures.
- Bells
- 3 metal, common manifold
- Pressure
- 120 PSI operating / 90 PSI restart
- Honk
- 4-5 s (127H) or 2-3 s (M3)
- Recovery
- ~35 s from 90 to 120 PSI
- Price
- $369.99-$399.99
What’s in the box
HornBlasters lists slightly different contents for the two variants. The 127H kit includes:
- Mini Outlaw train horn (black or chrome per SKU)
- HornBlasters 127H weather-resistant air source unit (2-liter compressor on a 1.5-gallon 4-port tank)
- Pre-installed 1/4-in. electric air valve
- 20 ft of 1/4-in. air line, plus an air line cutter
- 22 ft of 10-gauge red wire, 22 ft of 18-gauge blue wire, 22 ft of 18-gauge grey wire
- Complete wiring kit with fuse holder and fuses
- Mounting hardware, earplugs, and detailed instructions
The M3 kit swaps in the 3-liter compressor-and-tank combo, 12 ft of air line, an inline fuse holder, a toggle switch, a relay, and all electrical terminals, plus fittings and mounting hardware. Both variants ship with earplugs, which tells you something about the brand’s expectations for the horn.
Pros
- Genuine HornBlasters three-bell metal horn in a package two inches shorter and about four pounds lighter than the full-size Outlaw
- Honest spec sheet: HornBlasters publishes no dB number rather than inventing one, consistent with its public position on fake decibel ratings
- 127H variant is sealed against the elements on both the horn and the air system, so it can live under the vehicle
- Complete kit with a pre-installed electric valve, three wire runs, fuse kit, air line cutter, and hardware
- Owner feedback on hornblasters.com averages 5.0 out of 5 across 41 reviews at review time
- 2-year manufacturer’s defect warranty on the kit
Cons
- No published dB rating, test distance, or chord frequencies, so loudness cannot be compared on paper
- Roughly 35-second recovery after a 4-5 second honk (2-3 seconds on the M3): this is a burst horn, not a sustained one
- M3 variant’s tank-mounted compressor is not fully sealed and must be mounted upright in a dry enclosed spot or the warranty is void
- Detaching the compressor from the tank voids the warranty on either variant; HornBlasters points buyers who need a remote compressor to its 232-series kits
- 1/4-in. valve and air line limit airflow versus the 1/2-in. inlet on the full-size Outlaw
- Returns can carry a 15% restocking fee, and the 25% duty cycle means the compressor cannot be run continuously
Alternatives
- HornBlasters Outlaw 127H ($579.99 chrome / $599.99 black on the current Outlaw kit page). The full-size version of this horn on the same 1.5-gallon air system: 18.5 in. long, 15 lb horn, 1/2-in. air inlet. Our Outlaw 127H review covers why the extra bell length matters for tone.
- HornBlasters Flatlaw ($369.99 M3 / $399.99 127H). Same price ladder and the same two air systems, but the three bells are laid flat side by side so the horn is only 8 in. tall. See our Flatlaw review if height, not length, is your constraint.
- HornBlasters Outlaw 232 ($859.99). The heavy-duty Outlaw kit with a separate compressor and 5-6 seconds of honk, for buyers who want the compressor mounted away from the tank. Our Outlaw 232 review has the details.
For a broader comparison of the brand’s horn families, read our Outlaw vs. Shocker vs. Conductor’s Special guide.
Install / compatibility notes
The kit is a self-contained 12-volt system, so the vehicle only needs a healthy battery and a place to bolt things down. HornBlasters lists an 18-amp maximum draw, and the kit supplies 22 ft of 10-gauge red wire for the compressor feed. Our amp draw, fuse and wire gauge guide explains how to size the fuse and route that run. The compressor is rated for a 25% duty cycle at 100 PSI, which is fine for horn duty but rules out using the tank for tire inflation or air tools.
- Pick the variant to match the mounting spot. The 127H’s sealed air system can go under the bed or behind a bumper. The M3’s tank-mounted compressor is not fully sealed and HornBlasters says it must be mounted upright, enclosed, and away from moisture, dirt, and debris, or the warranty is void.
- Measure for the horn. It needs roughly 16.5 by 14.5 by 11 inches of clearance. Bells should point down or away from spray, and the kit’s bracket plate mounts to a flat surface.
- Do not separate the compressor from the tank. Both variants ship pre-assembled, and HornBlasters states that detaching the compressor voids the warranty.
- Run the 1/4-in. air line. The valve is already threaded into the horn, so you only run one line from the tank (20 ft supplied on the 127H, 12 ft on the M3).
- Wire it through the supplied relay and fuse. The kit provides separate 10-gauge power and 18-gauge trigger wires. Our relay wiring guide walks through the connections.
- Bench-test before the final fill. Expect a full fill from empty to take a little over two minutes at 13.8 volts, then about 35 seconds between honks. Our first-fill checklist covers what to watch for.
Vehicle-specific notes: the 1.5-gallon air source is 15.2 by 5.9 by 12.8 inches and weighs 13.75 lb, so it fits most full-size and mid-size truck beds and many SUV cargo wells. KT Performance lists the boxed kit at 38 lb shipping weight. Because HornBlasters publishes no dB rating, we cannot say how it compares to state noise caps on paper; read our legality guide before using it on public roads. Users installing on modern vehicles with body-control-module horn circuits should also see our CAN-bus guide, since this kit expects a simple switched 12-volt trigger.
Sources
- HornBlasters — Mini Outlaw Train Horn Kit (combined M3 / 127H page) — all four SKUs, prices ($369.99 / $399.99, compare-at $539.99), full spec tables for both variants, fill rates, included items, mounting and warranty conditions, in-stock status, 5.0/5 owner rating from 41 reviews
- HornBlasters — Mini-Outlaw 127H Train Horn Kit — single-variant 127H listing confirming $399.99 price, weather-sealed description, 4-5 second honk, 35-second recovery
- HornBlasters — Mini Outlaw 3 Liter Horn Kit — single-variant M3 listing confirming $369.99 price
- HornBlasters — Mini Outlaw Train Horn (standalone) — standalone horn SKUs AH-MC3 / AH-MC3B, $219.99, three metal bells, 1/4-in. air line
- HornBlasters — Outlaw Train Horn Kit — full-size Outlaw dimensions (18.5 x 15.5 x 12.5 in., 15 lb, 1/2-in. inlet) and 127H / 232 kit prices used in the Alternatives section
- HornBlasters — Why fake decibel ratings mislead buyers — brand’s stated position on not publishing inflated dB numbers
- KT Performance — HornBlasters Mini Outlaw 127H Series Train Horn Kit, Chrome — retailer price cross-check ($399.99), 120 PSI, 1.5-gallon tank, 38 lb shipping weight
Train Horn Hub aggregates publicly available data. We do not test products in-house. All trademarks belong to their respective owners.
The Mini Outlaw 127H is the right pick for drivers who want authentic HornBlasters three-bell tone in a truck, SUV or car where the full-size Outlaw won't fit — pay the extra $30 over the M3 for the sealed air system and the longer 4-5 second honk.
Frequently asked questions
Quick answers to the questions people ask most about this topic.
- How loud is the HornBlasters Mini Outlaw?
- HornBlasters does not publish a decibel rating, test distance or chord frequencies for the Mini Outlaw, and the brand has a public page explaining why it avoids inflated dB claims. It describes the horn as one of the loudest in its lineup, running three metal bells at 120 PSI, and includes earplugs in every kit, so treat it as genuinely loud but unquantified on paper.
- Which Mini Outlaw kit should I buy, M3 or 127H?
- We recommend the weather-resistant 127H kit ($399.99, SKU HK-MC3-127H chrome or HK-MC3B-127H black). It gives 4-5 seconds of honk on a 1.5-gallon tank versus 2-3 seconds on the M3's 3-liter tank, and its sealed air system can be mounted under the vehicle, while the M3's tank-mounted compressor must sit upright in a dry enclosed space or the warranty is void.
- How long does the Mini Outlaw take to recover between honks?
- Per HornBlasters' fill-rate table, both variants recover from 90 to 120 PSI in about 35 seconds at 13.8 volts. A full fill from empty takes about 2 minutes 10 seconds on the 127H's 1.5-gallon tank and about 2 minutes on the M3's 3-liter tank.
- How big is the Mini Outlaw horn compared to the regular Outlaw?
- The Mini Outlaw horn measures 16.5 by 14.5 by 11 inches and weighs 10.9 lb per HornBlasters. The full-size Outlaw is 18.5 by 15.5 by 12.5 inches and 15 lb, and uses a 1/2-inch air inlet versus the Mini's 1/4-inch line.
- What warranty comes with the Mini Outlaw kit?
- The kit carries a 2-year manufacturer's defect warranty plus HornBlasters' 30-day satisfaction guarantee, though returns may incur a 15% restocking fee. Detaching the compressor from the tank, physical damage, or mounting the M3 variant outside an upright dry enclosure voids coverage.
