To address your concerns, all I can say is that the warnings on the can are only the usual heat/puncture/incinerate/well-ventilated warnings on any aerosol can. Basically, it's just a can full of propellant. It's identical to the electronics cleaning/duster spray cans you can buy at an office supply store. I really don't think the amount expelled in a single spray is enough to be concerned about. It should be dispersed quite well. (And anyway, when the thing goes off, the cat immediately vacates the area
) As far as being set off by ANY motion, yes, of course, it doesn't discriminate. Strategic placement is required. That's why I thought it would be suitable for placing behind your computer. I don't think it really works very well for kitchen countertops.
I'll tell you what I ended up using as cat deterrent behind computer and stereo rack: the fluid in a Glade plug-in refill applied to a cotton swab. The one cat that likes to chew on cords HATES the smell!!
Of course, it does give a certain "citrussy" smell to the room. And that creates the situation of a smell unpleasant to the cats in part of their living area.
The reason I discontinued the ssscat is because two of the three cats are only afraid of the spray; they didn't learn to associate the whistle and aren't afraid of it. So I'd have to keep buying expensive refills indefinitely.