A TPMS is a genuinely useful safety net: it can catch a slow puncture on the highway before you feel it. But drivers over-trust it, and the two types behave very differently. Understanding how yours works — and where it goes quiet when it shouldn’t — is the difference between a helpful warning and false confidence. Here’s the plain-English version for Australian drivers.

What is a TPMS and what does it do?

A tyre pressure monitoring system alerts you, usually via a dashboard light or a pressure readout, when one or more tyres fall below a set threshold. The goal is safety and efficiency: under-inflation is the leading cause of tyre failure, and it quietly costs you fuel and tread life. There are two fundamentally different ways a car does this.

How does direct TPMS work?

Direct TPMS puts a physical sensor inside each wheel — usually on the valve stem — that measures the actual air pressure (and often temperature) and transmits it wirelessly to the car. Its strengths and limits:

• Accurate: reads real pressure, typically within a psi or two per wheel.
• Per-wheel: can tell you which tyre is low, and many show live psi.
• Battery-limited: internal OEM sensors last around 5–7 years and then need professional replacement; external screw-on aftermarket sensors use a replaceable coin cell (often 12–18 months).

How does indirect TPMS work?

Indirect TPMS has no pressure sensors at all. It uses the existing ABS wheel-speed sensors: a tyre losing pressure gets slightly smaller in rolling diameter and therefore spins marginally faster than the others, and the system infers a low tyre from that difference. It’s cheaper for the manufacturer and has no batteries to die — but it’s easily fooled.

Direct vs indirect TPMS: which is better?

When does a TPMS lie to you?

This is the part that catches people out.

• It warns late. OEM systems typically don’t light up until a tyre is roughly 25% below the recommended pressure — by then the tyre has already been running under-inflated and hot. A TPMS is a backstop, not an early-warning gauge.
• Indirect systems miss uniform loss. If all four tyres slowly lose pressure together — common over a season — there’s no speed difference to detect, so the light never comes on. This is why you still check pressures on schedule (see how often you should check tyre pressures).
• Indirect systems need resetting. After you adjust pressures, rotate tyres or fit new ones, an indirect system must be recalibrated or it reads from the wrong baseline.
• Cold mornings trigger it. Pressure drops with temperature, so a cool night can light the warning even on healthy tyres — see why your tyre pressure light comes on in cold weather.

None of this makes a TPMS useless — a direct system catching a highway puncture is a real safety win. It just means the dashboard light is the last line of defence, not the first. Your gauge, used on cold tyres against the placard pressure, is still the source of truth.

Is TPMS mandatory in Australia?

No. As of 2026 there is no Australian Design Rule requiring TPMS on passenger vehicles. Many new cars sold here have it anyway, because they’re built to United States or European standards where it’s mandated. So whether your car has TPMS — and whether it’s direct or indirect — depends on the model and where it was engineered for, not an Australian law.

What about aftermarket TPMS for 4WDs and caravans?

For touring, aftermarket direct TPMS is the practical choice. External screw-on sensors fit existing valve stems, display live pressures for every wheel, and many support separate on-road and off-road alert profiles — handy when you air down for the beach and back up for the highway. Systems that handle 8–10 sensors cover a vehicle plus a caravan or camper, closing a real gap for Australia’s towing culture. If you run aftermarket wheels, check sensor fit first — see TPMS sensors and aftermarket wheels. A monitor also pairs well with your compressor so you can watch pressures rise as you inflate, and it’s useful on a fully loaded road trip.

Frequently asked questions

Does a TPMS mean I don’t need to check pressures manually?

No. It warns late and (if indirect) can miss gradual, even loss. Keep checking with a gauge on cold tyres.

How do I know if my car has direct or indirect TPMS?

If your dash shows individual tyre pressures, it’s direct. If it only shows a warning light and you have to “reset” it after inflating, it’s likely indirect. Your owner’s manual confirms it.

Why does my TPMS light come on in winter but go off later?

Cold air lowers pressure; as the tyres warm with driving (or the day heats up) the pressure rises back above the threshold. Still, top up to the placard figure when cold.

Can I add TPMS to an older car?

Yes — aftermarket direct kits with external or internal sensors and a small display are widely available and are the go-to for 4WDs and vans.

Regulatory and technical details are current as a guide for 2026 — confirm specifics against your vehicle’s owner’s manual and the manufacturer.

Authority sources: Schrader TPMS — direct versus indirect TPMS.