Death by buzzer

No, Benz knows what they're doing. In a collision that bag could become a projectile so buckling it up reduces risk of.... oh I give up!

Or put it in the back seat or the cargo area. My Grand Cherokee also has a passenger seat weight sensor. Though it's not as obnoxious as the Mercedes since it just lights up a lamp on the center console but even my purse sets it off.
 
Another annoying part of these seat sensors is that it makes it impossible to tie in a rear facing car seat to the seat rails on the floor. I tried using the seat rail as an anchor point for the secondary upper tether on my son's car seat and it set off all the air bag warning lights on the dash. Very annoying.

Heidis, that design might be intentional - unless the airbag can be deactivated with a key switch (usually only in 2 seaters), a rear-facing child seat should *never* be placed in the front seat. The visor should have a big graphical warning.
  
My 3-series seems oddly more concerned about an unbelted pax than an unbelted driver. Being a seatbelt nazi, I actually mildly enjoy it when my pax takes his/her belt off while we're still rolling and the car goes nuts (after about 5 polite seconds). Saves me the trouble. :-)

Ask the Benz dealer if they can change the seatbelt warning settings. On my Toyota, the beep can be disabled so that you're left with just the flashing light if you put a bag on the front seat.

In my Honda Fit, if I put enough weight on the passenger seat, a warning light illuminates to indicate that the passenger-side airbags are off. If an actual passenger leans to the right, into the path of the side airbags, a different warning light indicates that those are disabled. (Neither light is the same as the one that illuminates if a person is unbelted.)
  
Sadly, I'm old enough to remember when Mercedes had a reputation for luxury and engineering.

kpschoedel, that feature you are speaking of on your Fit was introduced in a Mercedes-Benz, in the '90's. I don't understand why this irritates people so much. My Mercedes does the same thing but I just put my briefcase on the floor. When there is actually a passenger there that beeping is invaluable, as I have taken off driving before with my young nephew in the car compltely unaware he was not buckled up untl that beeping sound alerted me. I personally think it is a smart feature, I can understand why nearly every automaker has copied Mercedes on this.

Why can't they make the sensor weight sensitive so that it won't beep unless whatever is in the passenger seat is of a certain weight? Because a child who doesn't weigh much shouldn't be in the seat. So anything under 50 pounds or so must logically be a bag or a box of some sort. Could that work?
 
Regardless, I don't think its necessary. The people that say you should just put your bag on the floor should also be able to handle the suggestion that you have the presence of mind to make sure your passenger is buckled up, without needing an alarm to do it for you. One is just as easy as the other, but at least if the sensor isn't there then I don't have to worry about it screeching at me when I want to put a bag in the passenger seat.
 
I know its supposed to be a luxury car, but does it have to have this sensor? Does it make it seem less luxurious if your very expensive car becomes obnoxious? I don't know what to think... : )

Passenger seat sensors are actually weight-sensitive pads in many cars. I can put a bunch of things on the seat that don't set the warning off (food, laptop, etc). The weight reading is used to determine what intensity to fire the pax airbag, including not at all. It also uses seat position and belt usage in its calculation of the inflation intensity. So-called "smart" airbag systems are now federally mandated to help reduce the risk of airbag-related injuries.

Mercedesfan, my point was that the R500 evidently can't do what even my econobox can: distinguish between a bag of books and an actual passenger. If Mercedes did that in the '90s, why did they stop?

kpschoedel, I'm sorry I didn't mean to appear to be attacking your point, it was well made. Mercedes do, in fact, still have that feature the seats are just incredibly sensitive to any weight gain. I agree the system shouldn't be that sensitive, but Germans don't ever plan on anyone carrying anything but passengers (hence the lack of cupholders and storage). It is really more of a quirk than an annoyance in my opinion, that was all I was trying to say.

My laptop case weighs less than 20 pounds - much less than the threshhold of the softest smart airbag deployment. I have the same problem as Josh, and the same 80-minute commute. I want my stuff on the seat where I can get at it. Sunglass case, parking lot access badge, iPod, phone-charging cords - they're all in there.
 
Simply putting something on the floor isn't that much safer in an accident anyway. Side impacts and rollovers throw stuff all over the cabin regardless. The only real projectile protection is to put everything in the trunk or tie everything down. No more grocery shopping or Home Depot runs ever again in the R500 (or any trunkless vehicle) if we hold ourselves to THAT standard.

It's more convenient for me to just throw things on the passenger seat than in the passenger footwell. A carmaker shouldn't make me choose between the annoyance of a beep/flashing light and the inconvenience of digging things out the of the footwell. It's similar to what Donna DeRosa wrote about the Q7 insisting she keep washing her windshield. How annoying! If I couldn't find a way to disable those, I'd be questioning my purchase, especially of a vehicle as expensive as a Mercedes or Audi.
  
But then again, I'm the type of person that likes to be in control of my driving. I'd take a raw, primal vehicular experience over a pampered, isolated one any day. If all those little nuisance alarms come with it (put on your seatbelt, airbag is active, change your oil, wash your windshield, sit up straight, eat your vegetables), well, there'd better be a way to disable them. I'm not a little kid -- I don't need to be reminded of this stuff.