Most immobilizers wait for a restart. Idling trucks never give them one.
Nearly every immobilizer on the fleet market - including the big telematics brands - is a starter interrupt: a relay on the starter circuit that blocks the NEXT start attempt. It does nothing to an engine that is already running. That design has a blind spot the size of the trucking industry, because semi trucks idle - a lot.
| Starter-interrupt immobilizers | Horus 3800 active kill switch | |
|---|---|---|
| How it stops a theft | Blocks the starter - takes effect only at the next start attempt | Shuts the running engine down remotely once the vehicle is stationary - parked or idling |
| Truck idling at a stop | Unaffected - the engine is already running | Can be shut down and locked out on the spot |
| After the vehicle turns off | Prevents restart | Prevents restart too |
| Moving vehicle | No effect (by design, for safety) | No effect - engages only when the vehicle is stationary (by design, for safety) |
| Built for | Cars, loan recovery, vehicles that park and shut off daily | Tractors and straight trucks that run around the clock |
Total cost, one vehicle
| Samsara immobilizer stack | Horus 3800 | |
|---|---|---|
| Upfront, per vehicle | $79-$180 immobilizer + roughly $420 required Vehicle Gateway (public reseller pricing) | $100 activation - includes 24-month device rental, SIM, and setup |
| Monthly software | $27-$60+ per vehicle depending on plan | $30 per vehicle ($24.90 effective billed annually) |
| Contract | 3-year minimum; no month-to-month; early exit owes the remaining balance (per Samsara's own FAQ) | Month-to-month, 30-day notice |
| Fleets of 10 or fewer | All three years of fees due upfront | Same month-to-month terms at any size |
Fair context: Samsara sells a full fleet-management platform - cameras, ELD, maintenance - and if you already run it, the gateway is a sunk cost and the immobilizer is an inexpensive add-on. The comparison above is for a fleet buying immobilization as the goal. Prices are public reseller and vendor listings accessed July 2026; confirm current pricing with each vendor.
How starter-interrupt immobilizers work
The mainstream design - Samsara's Engine Immobilizer, Spy Spot's and Trackhawk's kill switches, and most others - splices a relay into the starter wire. Send the command and the vehicle cannot be started. Samsara's own documentation is explicit: if you disable a vehicle while it is in motion, the immobilizer takes effect only after the vehicle stops and turns off. Until the engine shuts down, nothing happens.
The idling gap
Long-haul tractors idle about 1,800 hours a year by Department of Energy estimates - overnight for heat in winter and AC in summer, and some drivers hardly ever shut the engine off at all. A thief does not need to start an idling truck; the hard part is already done. Climb in, release the brakes, drive away - and a starter interrupt never gets its moment.
What an active kill switch changes
The Horus 3800 kill switch acts on the running engine: once the vehicle is stationary - parked or idling - you can shut it down from your phone and keep it from restarting. It engages only when the vehicle is stationary and will never shut down a moving truck. The idling tractor at a truck stop, the unit warming up in the yard at 5am - those are exactly the vehicles it can protect.
The stack you have to buy
Immobilization from the big telematics platforms is an accessory, not a product. Samsara's immobilizer needs a Vehicle Gateway to function and a software license to control - roughly $500-600 of hardware per vehicle before the monthly fee, on a three-year minimum term. Horus ships immobilization as the core product: one device, no gateway, no add-on hardware, no license tiers. $100 activation with the hardware rental included, $30 a month, month-to-month.
Where starter interrupts still make sense
This is not a knock on the category. For passenger cars, buy-here-pay-here lending, and vehicles that park and shut off every night, a starter interrupt is a reasonable tool. The gap opens specifically where trucking lives: vehicles that stay running. If your equipment idles through the night, match the tool to the truck.
Sources
- Samsara Help Center - Engine Immobilizer (starter-wire interrupt; effective after the vehicle stops and turns off). Accessed July 2026.
- Samsara Help Center - Small Business FAQ (3-year minimum term; no month-to-month; 10-or-fewer fleets pay 3 years upfront; early termination owes the balance). Accessed July 2026.
- Public reseller listings for Samsara Engine Immobilizer and Vehicle Gateway hardware (LTT Partners, CDW, Sourcewell pricing documents). Accessed July 2026.
- U.S. Department of Energy / Argonne National Laboratory - long-haul trucks idle roughly 1,800 hours per year; rest-period idling for cab heat and cooling. Accessed July 2026.
- Trackhawk GPS - kill switch disrupts the starter to interrupt the ability for the vehicle to start. Accessed July 2026.
- Spy Spot - remote starter disable GPS tracker. Accessed July 2026.
Common questions
No — by design. It engages only when the vehicle is stationary — parked or idling, engine on or off. Unlike starter-interrupt immobilizers that only block the next restart, it can shut down a running engine once the vehicle stops moving. It's there to keep a vehicle from being driven away, not to stop one on the road.
Only the verified owner. We confirm vehicle ownership before every activation.
You'll have live location, movement alerts, and history — and our team works with you and law enforcement on recovery.
No. Month-to-month with 30-day notice. Annual billing saves 17% if you want it.