An entrepreneur is selling a small device that blocks the seat in front of you on an airplane from reclining. I think reclining seats are intruding on my tiny space, and I've been known to silently block the encroaching seat with my knees. Sometimes I'll even ask the person sitting there to warn me before reclining so I can prevent any damage to myself or whatever I have on the tray table, such as a laptop. So I'm sympathetic. But probably talking to the person is a better idea.
You can find out more at this site.