Airbag light comes on and stays on for...

[al]

When I start the car the airbag light comes on and goes off within 5-10 sec.  Today the light stayed on for approximately 30 sec and went out as I was driving down the road. It repeated this twice more, each time I started. 

I don’t have the fancy on-board diagnostics. 

I know the bag is at least 10 yrs old. Do I need to buy a new bag or send one of its components to someone to reset it?

The bag was not activated or minor bumps to bumper, I think.

Al
Honolulu