I like the war Mercedes does it. You have the light in the mirror, but if you turn on the turn signal and a car is in the blind spot, it doesn't just flash, you get an audible beep to warn you.
Side mirror caps with blind spot monitoring LEDs came in yesterday from zhong zhong. Gonna hand them off to have painted Dark Iron Blue; stock mirrors already have BSM so should be a fairly straightforward install (and curse @mr-fix for adding another project to my list.)
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