Warranty
The components in this kit are backed by a 2-year manufacturer's defect warranty.
HornBlasters · Flatlaw
Flatlaw Train Horn Kit
Air System
Horn Finish
Kit it out (optional add-ons)
+$39.99
+$42.89
+$189.99
+$66.60
2-year warranty
30-day money back
Everything included
The Outlaw sound. Eight inches tall.
The Flatlaw folds three train horn trumpets flat over a single mount, just 8 inches tall, so the classic Outlaw roar fits behind a grille, under a bed rail, or anywhere a bulky full-size train horn never could. Mount it out of sight and keep the full 120 PSI honk.
8″tall
17.5″long
16.25″wide
Built to disappear, not to whisper
Lays flat
Three trumpets nest over one mount at just 8 inches tall. It tucks into low-clearance spots a full-size train horn setup could never fit.
Real compressed air
A 120 PSI compressor and tank come in the box, and the system refills from 90 PSI in about 35 seconds between honks.
Everything to install
Air line, wiring, relay or full wiring kit, fittings, mounting hardware, instructions, and a set of earplugs. One box, one weekend.
Hear it at full pressure
One recording, no editing: the Flatlaw at its 120 PSI operating pressure.
Audio sampleFlatlaw train horn
0:000:00
Phone speakers undersell it. Earplugs ship in the box for a reason.
Pick your air system
Same Flatlaw horn either way. The air system decides how long you can honk, where the unit can live, and what else it can do.
Non-Weather Resistant (2-3 Seconds of Honk Time)
2-3 shonk time
~35 srecovery
$369.99kit price
The M3 packs a 3-liter tank and compressor into one unit about 16.5 by 4.9 by 7.1 inches. It is not weather sealed, so mount it upright in a dry, enclosed spot: behind a seat, in a trunk, in a toolbox. The smallest, simplest way to run a Flatlaw.
Weather Resistant (4-5 Seconds of Honk Time)
4-5 shonk time
~35 srecovery
$399.99kit price
The 127H is weather sealed, so it can live outside the cab: frame rail, truck bed, under the body. Its 1.5-gallon tank holds a longer honk, and the same air supply can top off tires or run small air tools.
Two finishes, one horn
Stealth Black hides in the shadows under your truck. Chrome wants to be seen. Same trumpets, same sound.
Stealth Black
Chrome
Everything in the box
Each kit ships complete and ready to install. The only difference is the air system.
Non-Weather Resistant (2-3 Seconds of Honk Time)
- Flatlaw train horn
- 3-liter compressor and tank combo
- Pre-installed 1/4″ electric air valve
- 12 ft of 1/4″ air line
- 22 ft of 10-gauge red wire, 22 ft of 18-gauge blue wire
- Inline fuse holder, toggle switch, relay, and electrical terminals
- All fittings and mounting hardware
- Detailed instructions and earplugs
Weather Resistant (4-5 Seconds of Honk Time)
- Flatlaw train horn
- HornBlasters 127H air source unit
- Pre-installed 1/4″ electric air valve
- 20 ft of 1/4″ air line
- 22 ft each of 10-gauge red, 18-gauge blue, and 18-gauge grey wire
- Complete wiring kit with fuse holder and fuses
- Mounting hardware and air line cutter
- Detailed instructions and earplugs
Full specifications
Non-Weather Resistant (2-3 Seconds of Honk Time)Part No. HK-F3B-M3 / HK-F3-M3
Horn
| Horn | Flatlaw train horn |
|---|---|
| Dimensions | 17.5″ L × 16.25″ W × 8″ H |
| Weight | 12.5 lb (5.67 kg) |
| Voltage | 12-volt DC |
Air source
| Unit | M3 3-liter compressor & tank combo |
|---|---|
| Operating pressure | 120 PSI |
| Restart pressure | 90 PSI |
| Unit size | 16.5″ × 4.9″ × 7.1″ |
| Drain port | 1/8″ NPT |
Fill rate (13.8 V supply)
| 0 to 120 PSI | 2 min (±10 sec) |
|---|---|
| 90 to 120 PSI | 35 sec (±5 sec) |
Weather Resistant (4-5 Seconds of Honk Time)Part No. HK-F3B-127H / HK-F3-127H
Horn
| Horn | Flatlaw train horn |
|---|---|
| Dimensions | 17.5″ L × 16.25″ W × 8″ H |
| Weight | 12.5 lb (5.67 kg) |
| Voltage | 12-volt DC |
Air source
| Unit | 127H weather-resistant air system |
|---|---|
| Air tank | 1.5-gallon (6.6 L), 4-port |
| Compressor | 2L, 18 A max, 25% duty @ 100 PSI |
| Operating pressure | 120 PSI |
| Restart pressure | 90 PSI |
| Unit size | 15.2″ × 5.9″ × 12.8″, 13.75 lb |
Fill rate (13.8 V supply)
| 0 to 120 PSI | 2 min 10 sec (±10 sec) |
|---|---|
| 90 to 120 PSI | 35 sec (±5 sec) |
On both kits, detaching the compressor from the tank voids the warranty. Need a split compressor and tank layout? Look at our 232 and higher models.
What owners say
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Before you buy
How long can I hold the horn?
The M3 air system gives you 2 to 3 seconds of honk per honk; the weather-resistant 127H gives you 4 to 5 seconds. Both refill from 90 to 120 PSI in about 35 seconds, so you are never waiting long between honks.
How loud is the Flatlaw?
We do not publish a dB rating for the Flatlaw, so we will not make one up. It runs real train horn trumpets on a 120 PSI compressed-air system in the same family as our Outlaw horns. Earplugs come in the box, and you will want them.
Will it fit my vehicle?
The horn needs a footprint of 17.5 by 16.25 inches and only 8 inches of height, plus a spot for the air system. It runs on 12-volt DC, so trucks, SUVs, boats, and RVs are all fair game.
Can I air up tires with it?
With the weather-resistant 127H system, yes: its 120 PSI supply can top off tires and run small air tools. The M3 combo is dedicated to powering the horns.
What do I need for the install?
Basic hand tools. The kit includes the air line, wiring, switch or wiring kit, fittings, and mounting hardware, and the electric air valve comes pre-installed on the horn. One caveat on the M3: mount it upright in an enclosed spot away from moisture and debris, or the warranty is void.
What is the warranty?
Every component in the kit is covered by a 2-year manufacturer's defect warranty, and the whole purchase is backed by our 30-day satisfaction replacement or refund guarantee.
Buy with confidence
Satisfaction guarantee
We offer a 30-day satisfaction replacement or refund guarantee on all purchases, except where otherwise noted in the product listing.
Money-back / refund policy
Merchandise may be returned within 30 days from the shipment arrival date for a refund. A Returned Merchandise Authorization (RMA) number is required for all returns, and a 15% restocking fee may apply. Please report any order discrepancy within 7 days of the invoice date.
Physical damage policy
Physical damage to any product voids warranty coverage. This includes improper handling and any damage sustained by irregular usage.
Mounting the 3-liter M3
The M3 combines the compressor and tank into a single unit that is not weather sealed, so it must be mounted upright in a dry, enclosed spot: behind a seat, in a trunk, or in a toolbox, away from moisture, dirt, and debris. Mounting it any other way, or separating the compressor from the tank, voids the warranty.
California Proposition 65 Warning
This product can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov.
Hearing protection recommended
These air horns are extremely loud. Wear hearing protection when testing at close range, never honk directly next to a person or inside an enclosed space, know your local regulations, and use the horns responsibly.
Fits where nothing this loud should.
The Flatlaw Train Horn Kit ships complete, installs with hand tools, and is backed by a 2-year warranty and a 30-day money-back guarantee.