They do - at a certain weight level, but the kit adds a key to disable and the latch hooks in the front seat which make it easier to secure the car seat as well as being able to completely disable the airbag regardless of current weight in the seat.
Hmm...the light in my 06 turns on when I put my work gym bag in the seat, which weighs 25 pounds tops.
That's correct. 25 pounds is less than 90 pounds. The bag weights enough for the system to know that something is in the passanger seat, but not big (heavy) enough to activate the air bag.
After enjoying the continous air bag light on our 01' S, I thought I had escaped air bag warning lights on the recently acquired '07 S. When the passenger seat is empty, the "air bag off light comes on" and the info screen has a warning the, "p. a. b. is stuck, check passenger airbag settings." It continues to flash the warning during the passenger less drive. No problems when a passenger is seated and properly belted. Any thoughts?