Passenger light for airbag won't go off

I was under the impression that the passenger airbag indicator light only came on when it sensed a certain amount of weight on the seat. For the last couple of days the light has been on even though there is nothing on the seat. Anyone else ever have this problem?

Also while we're on the subject of lights that I don't remember seeing always coming on, what's the deal with the little flashing car with the key symbol on it? I never noticed this before but it seems like it's always on when the truck is off. It blinks every 3 or 4 seconds. I had never noticed it before and there happened to be a Tacoma in the parking lot right next to mine so I looked in the window and their light was not flashing or even on. Is this for the alarm or something?

 

On my 05, if the seat has no weight in it, the light is off. But add some weight (ammo can of 30-06) the light comes on. Don't know the exact weight.
As for the other question, no clue don't have the issue...sorry.

 

There is a switch that I can turn the airbag off and on with the key, but I leave it on all the time. I just didn't know why the light came on with nothing on the seat when I don't ever remember it being on before.

What is the engine imobilizer system and why does it function when the car is off?