Ignition on and off: 1 true signal and its 4 false versions
In short
An ignition event is a timestamped state change saying a vehicle was switched on or off, and its value depends on where it came from. Four mechanisms produce it — a hardwired splice to the ignition circuit, a parameter from the vehicle bus, a voltage threshold, and inference from movement — and most platforms flatten all 4 into 1 boolean that never says which.
Key takeaways
- Ignition on, engine running and moving are 3 states. Most feeds report 1 flag for all 3.
- A hardwired sense wire is the cheapest true signal — if the installer found the switched circuit.
- Voltage-inferred ignition misreads a yard charger, a jump start and 24-volt vehicles read on 12-volt limits.
- Movement-inferred ignition reports off while idling and on while being towed. Both errors cost money.
- Record provenance per device. One boolean across a mixed fleet cannot be audited or corrected.
An ignition event is a state change with a timestamp and a position: the vehicle went off to on, or on to off. It is the cheapest useful signal in a fleet, because almost everything downstream — cadence, idle time, trip boundaries, detention clocks — keys off it. Its worth depends on which of 4 mechanisms produced it, and the field arriving in your platform rarely says.
Start by separating 3 states one boolean cannot express. Ignition on: the key energises the circuits. Engine running: combustion, or the traction system live. Moving: the vehicle has road speed. A truck idling at a gate is on, running, not moving. One on a transporter is off, not running, moving at 90 km/h.
Four mechanisms, four different truths
| Source | What it measures | Says ON when the engine is off | Says OFF when the engine is on |
|---|---|---|---|
| Hardwired sense wire | Voltage on a circuit live only with the key turned | Key at accessory, radio or heater on, or a splice into a live circuit | Rare: a failed splice, not a logic error |
| Vehicle bus parameter | Engine state or speed reported by the vehicle itself | Almost never: this is the authoritative reading | Bus asleep, or the parameter unpublished on that make and year: silence reads as off |
| Voltage threshold | System voltage above a charging threshold | Yard charger, jump start, or a 24-volt vehicle read on 12-volt limits | Failing alternator, heavy load at idle, cold-start sag |
| Movement inference | Accelerometer activity or change in position | Towed, on a ferry or transporter, or scatter while parked | Idling at a gate, working at standstill, or queueing |
| Provider-normalised flag | Whichever of the above the device had, flattened server-side | Inherits every error above with no marker of which | Inherits every error above with no marker of which |
The last row is the one that hurts. One field name across a mixed fleet, produced by 3 mechanisms on 3 hardware generations, is a field nobody can correct — the same disease as a carrier code whose meaning depends on who populated it, described in 4 letters that are supposed to identify a carrier.
The install decides the signal, not the specification
A handset has no ignition circuit at all, so a phone-based feed has only movement inference or a Bluetooth pairing event — a limitation to weigh in installed unit or the driver's phone. Movement inference also drags in position scatter: a parked vehicle whose fixes wander appears to move, the noise map matching turning pings into roads exists to absorb.
What each error costs downstream
- Idle time becomes fiction. A movement-inferred flag records off while an engine idles, so idle reporting is blind to the case it exists to measure.
- Detention clocks start late or never, because the flag stays on while the heater runs.
- The map freezes. Most platforms drop cadence to a heartbeat on ignition off, so a false off leaves a moving vehicle still on screen — 1 cause behind vehicles frozen on the live fleet map.
- Movement with the engine off is misread. A recovered vehicle reports a working trip, and mileage, hours and utilisation absorb it.
- Cold mornings generate phantom events: a start-up sag crosses the voltage threshold, emitting an off and an on inside 10 seconds, so winter trip counts rise.
Ignition is the field everyone trusts and nobody can trace: 1 boolean standing in for a wire somebody chose under a dashboard 3 years ago.
What to establish before trusting the field
- Ask the provider which mechanism produces the flag per device model, and store the answer on the vehicle record, not in a document.
- Sample 5 vehicles and compare ignition against speed for a week. Movement inference shows immediately: ignition on and speed above 0 always coincide, which real ignition never does.
- Look for events shorter than 20 seconds: a cluster means a voltage threshold crossed by noise, not by a driver.
- Compare idle minutes across vehicle types: a group reporting almost no idling is inferring ignition from movement.
- Where the bus parameter exists, prefer it and keep the sense wire as fallback. Two sources that agree beat 1 nobody can check.
None of this makes ignition a bad signal. It is the cheapest true thing a vehicle will tell you, and recording provenance per device gives a state model that can be corrected rather than argued about. Building that model and the alerting on it is the work we describe under AI agents and workflow automation, with the context in AI in logistics operations. Neighbouring definitions sit in telematics and the live vehicle data plane, inside our logistics and mobility work.
Frequently asked questions
Short answers to the follow-ups this page tends to raise.
What does an ignition on/off event mean in telematics?
It means the tracking device observed a change in the vehicle's power state and recorded it with a timestamp and position. What that rests on varies: a wire spliced into the ignition circuit, a bus parameter, a voltage threshold, or an inference from movement. The event name is identical in all 4 cases; the reliability is not.
What is virtual ignition, and when is it acceptable?
Virtual ignition is a state inferred from movement or accelerometer activity rather than measured from the vehicle. It is fine where the only question is whether the asset moved — trailers, plant, unpowered equipment — and unacceptable wherever idling, detention or engine hours matter, because it reports off for a stationary running engine and on for a towed one.
Does ignition on mean the engine is running?
No. Ignition on means the circuits are energised, which includes a key turned without the engine started and, on many installs, the accessory position too. Engine running is a separate fact, reliable only from the vehicle bus. Treating them as identical produces idle figures operations staff know are wrong and cannot explain.
Why does the same fleet report wildly different idle times by vehicle?
Usually because the vehicles are not measuring the same thing. Units wired to a switched circuit report genuine idling; units inferring ignition from movement report almost none, because a stationary vehicle looks off to them. Group vehicles by how the flag is produced before comparing.
- ignition
- telematics
- vehicle state
- device install
The work behind this page
Builds from our portfolio that this page draws on.
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