Our long-term 2009 Audi S5 is equipped with a blind-spot detection system (named, somewhat confusingly, Audi side assist). It's part of the Tech package ($2200) that includes back-up camera, adaptive headlamps (AFS), and smart keyless entry/start.
If another vehicle is in your blindspot (either side), the dots in the respective mirror housing light faintly (above pic). Signal a lane change while the other vehicle is there and the dots flash. Audi says the system range is 150 ft and your car must be going at least 19 mph. There is no auditory alert.
If you aren't aware of the system, the first time it flashes you may think you ran a traffic camera.
Or that perhaps paparazzi were interested in your business.
What's that? You don't like it because you're a Luddite?
There's a defeat switch near the A-pillar above the speaker.
Albert Austria, Senior Engineer, Edmunds, Inc.

cwmoo740 says:
04:32 PM, 10/15/09
That's a better approach than the stupid beeping ones, but it might still annoy me. PAMs are much less intrusive.
SnakeDoctor says:
04:41 PM, 10/15/09
moo -
I'm not familiar with the term PAM. Please enlighten me.
Thanks,
Albert
smrtypants44 says:
05:15 PM, 10/15/09
Do both the LEDs in the mirror housing and the off/on switch blink? Or is the on/off switch blinking just a visual artifact?
altimadude00 says:
06:38 PM, 10/15/09
This stinks along the likes of the Department of Redundancy Department. If you have the mirror adjusted properly to view the blind spot, and you remember the check the mirror and over your shoulder, then you can save yourself the expense of such a system. I'm glad it has an off switch and I'm glad it doesn't beep. It would be off in my car.
cwmoo740 says:
07:25 PM, 10/15/09
I believe someone else used it here before - Properly Adjusted Mirrors.
carguy622 says:
07:27 PM, 10/15/09
I was passing a Fusion hybrid a couple of days ago and noticed that the side view mirror had Ford's version of this, and it lit up. Kind of cool.
@altimadude00: I agree that adjusting your mirrors and glancing over your shoulder takes care of most of this. But I think these systems could be helpful in a car with poor visibility, like a convertible. I was driving the Miata in Manhattan last friday, and while I have my mirrors adjusted properly and I looked out the windows, I managed to drive into someone. I lost a Jeep Wrangler in the fabric top. This feature would have provided an additional caution and may have prevented that.
altimadude00 says:
08:44 PM, 10/15/09
Carguy--I suppose it depends on the situation and what car you're driving. I can only say what's worked for me. A system like this would be wasted on me, but a key component to someone else. I guess anything helps in these days of shrinking glass, widening pillars, and rising window sills.
stovt001 says:
10:00 PM, 10/15/09
Blind spots only exist where mirrors are improperly positioned.
lvgti says:
08:22 AM, 10/16/09
Here's a simple & cheap solution....in addition to PAM, also use 3" spot mirrors. I've been using 'em for 40 years. The only time I shoulder check is when it's raining. As for safety, I've been driving more than 50 years & have never had a "chargeable or at fault" accident. Oh, and those 50+ years have been spent driving in SoCal, Vegas & many cross country trips.
boxermike says:
10:25 AM, 10/16/09
"cwmoo740 says:
07:25 PM, 10/15/09
I believe someone else used it here before - Properly Adjusted Mirrors.
"
I lol'ed. I'm going to use that daily.
-mm
hondacura4 says:
12:50 PM, 10/16/09
What ever happened to just paying attention to your surroundings and using your mirrors? The R&D investment spent on "technology" like this could be put elsewhere in the vehicle.
cr_driver says:
06:04 PM, 10/16/09
Nicely done