I know a lot more about smoke detectors than most humans should, and it's not possible to say how sensitive it is. Some are quite sophisticated and will only go off if there is actual smoke in the room, others will go off if there's steam or stuff like deodorant in the air. Similarly, each manufacturer will use a different algorithm for signalling alarms, plus there's tolerances in the components AND variations in the quality of air flow in the detector, and this varies between each detector depending on the conditions it's put in. In a kitchen it might be less sensitive due to a build up of grease/fat.
My inkling would be that if making a couple of slices of toast or cooking in a pan normally doesn't set it off then the George Foreman grill should be fine.