My airbag on my 2012 Honda Civic goes off and on every 5 seconds?

If I turn on the car with someone sitting in the passenger seat my car alerts me every 5 seconds that the airbag is off then on then off then on for the duration of my drive. It is really annoying because it beeps while its doing this. However if I turn on the car wait 30 seconds and then someone sits inside this problem doesn't happen. What can I do to fix it? I took it to Honda and they can't seem to find the problem. They changed all the sensors already.

*I was in a car accident prior to this. Airbags never come out

Cars equipped with modern two stage airbags have a sensor in the seat that does one of three things all the time. If nobody is sitting in the seat, as measured by a sensor like a bathroom scale, then the airbag on the passenger side will not go off in an accident saving a lot of money in post crash repairs. Should baby seat be hooked in that seat, it would be bad if it went off. Also, a young 80 plus pound child doesn't need the full power blast from the airbag because it won't then be soft enough to do a child much good so the depowered deploy works best. Third, the airbag does it's normal parlor trick for adult passengers in the seat.
If you have a person in the seat that happens to be at or near the weight causing the airbag to arm and disarm as you ride down the road, that could theoretically cause your problems.

Is there more than one Honda dealer in your area? This is a lifetime warranty item and a safety device. It needs to be fixed by them no matter what. If you aren't satisfied then someone higher than the dealership needs to get involved.