Seat belt warning light
A seat belt is not fastened. UN R121 makes the seat-belt tell-tale red. FMVSS 101 lists the front seat belt unfastened telltale in Table 2 (symbol, or the words “Fasten Belts” / “Fasten Seat Belts”) and leaves its details to FMVSS 208.
Red
What to do
Fasten the belt, and make sure passengers do. If the lamp stays on with every belt fastened, a buckle or seat sensor may be at fault — have it checked, and see the manual for which seats the car monitors.
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
- Seated person with a diagonal belt
- 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 |
|---|---|---|
| FMVSS 101 | Table 2, “Front Seat Belt Unfastened Telltale” — words “Fasten Belts” or “Fasten Seat Belts” | no colour in Table 2; see FMVSS 208 |
| UN R121 | Table, item 21 “Seat belt” — tell-tale | red |
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. 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.
Good to know
- FMVSS 101 Table 1 also has a “Rear Seat Belt Warning” telltale: green where it shows which rear belts are in use, red where it shows belts not in use or unbuckled (note 21).
Other red lights
Sources
- 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
- 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
- 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.