TheSagaContinues

One of my players will be playing a 3rd-degree droid, and I need to understand behavioral inhibitors better. What exactly can such droids do in combat, and what can they not do?

-Can they blast someone with a blaster set on stun? I assume it hurts, but it won't cause permanent harm.
-Can they be as violent as they wish against other droids?
-Can they defend themselves or their friends against beasts, who are living but non-sentient? Can they use lethal force against them?
-Can they shoot vechiles with sentinents inside with ion cannons?
-Can they shoot vechiles with sentients inside with blasters/lasers if it seems likely that the shot will only stop (disable) the vechile and not harm those inside?
-etc!

What kind of processor will the droid have? If a basic one, I´d say it can´t do much. On the other hand, with heuristic processor, he can circumvent his inhibitors by "creatively interpreting its instructions" (SECR p. 190). Thus, if the droid can come up with plausible logical reason, he can do pretty much anything per rules. Of course, I´d suggest some test, maybe Int with DC set by the severity of the actions (I believe there was something like this in RCR, but I´m not sure)

Shooting anyone with stun is legal, as you put him out of harm´s way (he would be killed if he continues to attack your less-inhibited friends).
Shooting droid is legal (they´re not sentient and if they´re attacking sentients, destroying them is basically the same as destroying the blaster they´re pointing at someone).
Defending sentients against beasts is legal. Defending self or other droids is a bit trickier, but good reasoning could get you there (by protecting yourself you can later protect sentients), but that could call for the test
Shooting vehicles with ion cannons... that depends on circumstances and reasoning... shooting a swoop in a chase is no - the driver would die in a crash. But shooting at a TIE fighter is legit (with a test maybe) - there is definitely someone close to save the pilot, who will have several hours of life support, not to mention a chance to jury-rig the ship back online.
Shooting vehicles with lethal damage is questionable, but I would allow it with clever reasoning and Int test DC 15-20 or so.
StevenO - the argument with BBEG is not valid. BBEG is a living being, and droid character (unlike his player) doesn´t know he can´t kill him with a shot - he doesn´t know anything about HP and treshold, only that he could drill a hole in his chest or head with blaster. On the other hand, the droid can very well be avare that even with a lucky hit, he is unlikely to destroy a corvette with a signle shot from starfighter-class blasters, even with a lucky hit

Note on the side - the inhibitors are removed with a single level of Independent droid, which can be as soon as 4th lvl

Basically, you´re right. Point is, by the rules there is not much the droid can´t do under certain circumstances and with good wording. It´s up to the player and GM what they allow and how they play the game. I was trying to show that there is not much stricktly forbidden. I once played a snapped medical droid that enjoyed inflicting pain upon organics. And I do believe it was all right, as the droid played was consistent. It always took delight in hurting organics, even while Treating the injuries. If I played a normal medical droid, trying to avoid any harm to sentients, and suddenly decided to shoot the thugs to speed things up, that would be wrong. (Side note - if such a help from the said droid would mean a difference between life and death of some other PC, I´d allow it, but give the droid some adequate quirk to represent the damage this caused to his logic)
I also see nothing wrong if a mining droid adds organics to his minig protocol (KotOR2 reference here) - if it is consistent.

Bottom line: Droid with heuristic processor has few real limitations, and Independent droid is the same as any organic sentient - RULEWISE. Thus, it really boils down to what the player wants, and what GM allows. And, of course, roleplay and having fun

One thing I might add when it comes to interpreting a Behavioral Inhibitor is just the question of how you are handling DSS increases.  If the GM is handing out increases in a DSS for most anything then it better be darn near impossible for the droid to break the Inhibitor.

Huh, it didn´t occur to me, but now that you said it, it looks really obvious. After all, Inhibitors are sort of a "hard-wired moral code" of the droids. It might make a good lead on how to deal with it - anything rising DSS should be next to impossible under normal circumstances for a non-sentient droid (sentient droid should have same limitations as sentient organics, in my opinion, gaining DSS and probably quirks when violating the Inhibitors)