Both green indicator arrows on your dashboard are flashing at the same time, and a red triangle button is illuminated. This is the hazard lights indicator. Most drivers know roughly what hazard lights are for, but fewer know exactly when they should and should not use them, or that leaving them on while parked can leave you with a flat battery. This guide covers everything you need to know.
What Does the Hazard Lights Indicator Look Like
The hazard lights are activated by a button, usually the largest and most prominent button on the centre of the dashboard or the centre console, marked with a red triangle symbol. When the hazard lights are active, both the left and right green indicator arrows on the instrument cluster flash simultaneously, and the red triangle button itself is usually illuminated to show the system is active.
On the outside of the car, all four indicator lights, front left, front right, rear left, and rear right, flash together in unison. Most cars also produce the same audible clicking sound that the turn signals make, but from both sides at once.
What the Hazard Lights Are Actually For
Hazard lights exist for one primary purpose: to alert other road users that your vehicle is a potential hazard in an unusual or unexpected position. They are a warning to other drivers, not a communication tool for convenience or frustration.
The key distinction is that hazard lights are for use when the vehicle itself is the hazard, not when traffic conditions are hazardous in general.
When You Should Use Hazard Lights
Broken Down or Stopped in a Dangerous Position: If your car has broken down and is stopped on the hard shoulder, on a narrow road, or in any position where other drivers may not expect a stationary vehicle, switch your hazard lights on immediately. This is the primary and most important use. The flashing lights warn approaching drivers that there is a stopped vehicle ahead and give them time to slow down or change lanes.
Towed Vehicle: If your car is being towed using a tow rope, hazard lights on the towed vehicle help alert other drivers that the vehicle is moving unusually slowly or unpredictably. Many countries require hazard lights to be active during a tow rope situation.
Warning of a Sudden Queue Ahead: In some countries, briefly flashing hazard lights while slowing down rapidly on a motorway is used to warn following traffic of a sudden queue or hazard ahead. This is a brief flash, not a sustained use while moving at normal speed.
Slow Moving Vehicle in a Hazardous Location: A vehicle moving significantly slower than surrounding traffic due to a serious fault may use hazard lights to warn faster approaching traffic as a last resort when pulling over is not immediately possible.
When You Should Not Use Hazard Lights
Double Parking or Briefly Stopping in a No-Stopping Zone: Using hazard lights to justify parking illegally, stopping on a yellow line, or blocking a junction is one of the most common misuses. Hazard lights do not make an illegal stop legal, and in many countries this is a specific traffic offence.
Driving in Heavy Rain or Poor Visibility: Some drivers activate hazard lights in heavy rain while still driving at normal speed, believing this makes them more visible. This is actually counterproductive and in many countries illegal while driving. Flashing hazard lights while moving cancel the ability to signal turns because both indicators are already in use. Other drivers cannot tell which direction you intend to go. Your headlights and rear fog light are the correct response to poor visibility.
General Traffic Conditions: Using hazard lights in slow-moving traffic does not serve a useful purpose and limits your ability to signal lane changes. Regular brake lights are what following drivers watch when traffic slows.
Hazard Lights and Battery Drain
Hazard lights draw significant power because they flash all four exterior indicator bulbs simultaneously. If left on with the engine off, they will drain the battery. Most batteries can be significantly drained within two to four hours, and a weak battery can be rendered too flat to start the car in even less time.
If you use hazard lights in a breakdown situation and then wait for roadside assistance, be aware of the time. Consider turning them off periodically to preserve battery charge if the location is safe enough to do so.
After any situation where hazard lights have been on for an extended period with the engine off, start the engine and drive long enough to allow the alternator to recharge the battery before parking again.
Hazard Lights Not Turning Off
If the hazard lights are on and the button does not turn them off, the button itself may have become stuck in the depressed position, or the switch contacts inside the button may have developed a fault. Try pressing the button firmly several times. If the lights remain on despite the button appearing to be in the off position, a wiring fault or a stuck relay is the likely cause, and the car needs to be checked by a mechanic.
Hazard Lights While Driving
The legality of using hazard lights while the car is moving varies by country. In the United Kingdom, hazard lights while moving are permitted only briefly to warn of a sudden hazard on a motorway. In Germany, brief hazard flashing while braking hard is accepted practice. In many other countries, using hazard lights while driving at normal speed in rain or traffic is against the law.
As a general rule, if the car is moving normally, hazard lights should not be on. If the car is barely moving or stationary in a dangerous position, hazard lights are appropriate.
How To Turn On and Off Hazard Lights
The hazard light button is usually the most prominent button on the central dashboard, always marked with a red triangle. Press it once to activate. Press it again to deactivate. The button is usually illuminated red when the hazard lights are active.
The hazard lights remain functional even with the ignition switched off on most vehicles so that a broken-down car can use them without keeping the ignition on. This is also why they can drain the battery if left on.
Quick Summary
|
What |
Detail |
|
Light Color |
Both green arrows flash simultaneously, red triangle button illuminated |
|
Button Symbol |
Red triangle |
|
Correct Use |
Broken down, towed, sudden queue warning, slow-moving hazard |
|
Incorrect Use |
Double parking, driving in rain, normal slow traffic |
|
Key Risk |
Battery drain if left on with engine off |
|
Works With Engine Off |
Yes, on most cars |
Related Indicators and Lights
- Turn Signal Indicators – Individual left and right arrow indicators and bulb faults
- Charging System Warning Light – Battery and electrical system warning from drain
- Low Beam Indicator – Correct response to poor visibility instead of hazard lights
- Auto Headlight Indicator – Automatic lighting system for visibility in poor conditions
This page is part of our complete guide to car dashboard symbols and meanings. To see every warning light explained in one place, visit our Car Dashboard Symbols.