Blind spot monitor light

The blind spot monitor watches the lanes beside and behind you with rear-corner radar. The light comes on when a vehicle is in your blind spot. On some makes it is a symbol on the instrument panel; on others it is a lamp in the door mirror.

Yellow / amber

Not defined by regulation: a maker convention

What to do

Look in the mirror and over your shoulder before changing lanes, and do not move over while it is lit or flashing. It is an aid, not a guarantee: Hyundai's manual notes the radar can miss a car in the next lane on a wide road and warn about cars two lanes over on a narrow one. If it stays on with nothing beside you, clean the rear bumper corners, and have it checked if it persists.

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: Two cars side by side with signal waves between them
Colour: Yellow / amber
Standard: None — a maker convention, described here from 2 makers: Volkswagen, Hyundai

Where makes differ

Volkswagen shows an amber blind-spot symbol that also lights briefly to say the system is ready, and stays lit if a vehicle is detected. Hyundai puts the warning light in the outside mirror (and head-up display), lights it above 20 km/h (12 mph) when a vehicle is detected, and blinks it with a chime if you signal towards that vehicle above 40 km/h (25 mph).

Not defined by regulation: a maker convention

Neither US FMVSS 101 (Tables 1 and 2) nor UN Regulation No. 121 lists this light, so no rule fixes its symbol or its colour. What follows is what the makers cited below say; other makes, and other model years of the same make, may draw it differently.

Neither FMVSS 101 nor UN R121 lists a blind-spot tell-tale.

Other yellow / amber maker lights

Diesel particulate filter (DPF) lightBox full of dots with a pipe at each end · maker convention AdBlue (DEF) warning lightLiquid container with a wavy fill line and a drop · also red · maker convention EPC (electronic power control) lightThe letters EPC · maker convention Lane assist (lane keeping) lightLane markings running away from you, dashed line in the middle · also green · maker convention Forward collision warning lightCar seen from behind with radar arcs around it · also red · maker convention Adaptive cruise control (ACC) lightSpeedometer dial with a needle · also green · maker convention Auto Hold lightThe words AUTO HOLD · also green · maker convention Power steering warning light (EPS)Steering wheel, sometimes with an exclamation mark · also red · maker convention Water in fuel light (diesel)Fuel pump with water drops beside it · maker convention Gearbox (transmission) warning lightCog wheel with an exclamation mark · maker convention Key not detected lightKey with a question mark · maker convention Bulb failure (exterior light) warningLight bulb with rays and an exclamation mark · maker convention Hill descent control lightCar pointing down a slope · also green, red · maker convention Auto stop-start lightLetter A inside a circular arrow · also green · maker convention

All yellow / amber dashboard lights, regulated ones included

Sources

No regulation defines this light, so it is described from 2 carmakers' own manuals or owner pages, each fetched and checked on the date shown:

Volkswagen: Volkswagen UK — Blind Spot Monitor (amber) (amber lamp) — Lights briefly when activated and ready; stays lit when an object is detected in the blind spot; if it stays on constantly, contact a repairer. checked 2026-09-24
Hyundai: Hyundai owner's manual, 2025 Tucson (general market) — Blind-Spot Collision-Avoidance Assist operation (Collision warning (while driving)) — The warning light on the outside rearview mirror lights when a vehicle is detected (above 20 km/h) and blinks with an audible warning if the turn signal is on towards it (above 40 km/h). checked 2026-09-24

Written in our own words; the makers' pages cover their own models only.