It should automatically be disabled if the weight isn't met. My wife while sitting in the front seat has done it a few times while moving around and leaning over to deal with the kids in the back, I get a message in the evic saying that the passenger side air bag or wherever is off. Yeah, I actually think it goes so far as to disable the front one, or the side depending on what it's sensing. Airbags are dangerous if you aren't seated properly. Double check your manual, but this has been true on all of my recent vehicles.
2013 RAM 1500 Laramie Longhorn - Black Gold Pearl with all the trimmings. HEMI, 3.92, 8-Speed and Air Suspension
14" Magnaflow, BAK FiberMax Tonneau, Misc Whelen Emergency Lights and Switchpak, 275/60R20 - BFG T/A KO2