Hazard warning light
The hazard warning lights are on: all the direction indicators are flashing together. UN R121 makes the hazard tell-tale red.
Red
What to do
Switch the hazard lights off with the triangle button once the hazard has passed. Use them when your car is itself a hazard to others, for example stopped where it should not be.
Makes differ: what this light means on your car, the other colours it may use for the symbol and what the car wants you to do are set by the manufacturer, so your car's owner's manual is the authority.
- Symbol
- Triangle inside a triangle
- Colour
- Red
What the colour means
Red — “danger”
The colour code that UN R121 points to (ISO 2575, paragraph 5) is sold, not published. The EU wrote it into law for two- and three-wheel vehicles in Directive 2009/80/EC, Annex I, 2.1.4: “red: danger”. FMVSS 101 does not define colour meanings, but S5.5.6(b) says a telltale for which red is required must not be cancelable while its underlying condition exists, and note 4 to Table 1 allows red to be red-orange.
Where the regulations list it
| Rule | Row | Colour it sets |
|---|---|---|
| UN R121 | Table, item 6 “Hazard warning signal” — tell-tale | red |
| FMVSS 101 | Table 1, “Hazard warning signal” — telltale | no colour required |
UN R121: Cars (category M) and light goods vehicles (N1) type-approved under the UN 1958 Agreement, which includes the EU, UK and Japan (para 1). Its table gives the symbol and colour of each tell-tale; note 2 says the symbols are substantially identical to those of ISO 2575:2004. FMVSS 101: Passenger cars, multipurpose passenger vehicles, trucks and buses sold in the US (S3). Table 1 gives the symbol or words and, where one is required, the colour of each telltale; Table 2 lists identifiers with no colour requirement.
Good to know
- A separate hazard tell-tale is not required when both turn-signal arrows flash together to show it (UN R121 note 4, FMVSS 101 note 7), so on many cars you will see two green arrows instead of a red triangle.
Other red lights
Sources
- EUR-Lex — UN Regulation No. 121 (01 series), Official Journal of the EU L 5, 8 January 2016: table 'Symbols, their illumination and colours' — checked 2026-09-23
- eCFR — 49 CFR 571.101, Standard No. 101; Controls and displays (current text) — checked 2026-09-23
- govinfo — 49 CFR 571.101 in the Code of Federal Regulations, 1 October 2025 edition (Tables 1 and 2 as printed) — checked 2026-09-23
- Directive 2009/80/EC, Annex I, point 2.1.4 — the tell-tale colour meanings as written into EU law (for two- and three-wheel vehicles) — checked 2026-09-23
Meanings are written in our own words from these public texts, not quoted from ISO 2575, and were checked on the date shown.