SoSac would be insanely OP with this, tripwire and some SoSac is enough to kill a FG. I also don't think poison should count, since it doesn't target anything.
Taking these cards out of the picture would make this more balanced (at least SoSac) and it could be great for bluffing too.
Cards such as Heal and SoSac are
not redirected to the opponent. They, for the purposes of the card, always target you. Which is why poison counts: For the purposes of the card, it always targets your opponent.
(... Unless you can target SoSac when you normally play it, in which case I have no idea what to do.)
I assume it has to be possible to target the spell.
What happens if the opponent tries to destroy this? or even steal it...
Not sure. Do you think it should trigger before or after? I mean, it's a tripwire, so logically if you tried to blow it up...