SilverWook said:.
2. Arguably, the trash compactor system is automated. Otherwise, somebody would have overridden Artoo's ability to shut it down, let alone open the hatc
The homing beacon plan could have been hatched and implemented only a short time before the gang got back to the docking bay. The ship was lightly guarded, and the troops present didn't interrupt Vader's duel. Those particular troops may have been the only ones with specific instructions not to hit anything.
Hmm, this assumption rests on shaky ground: the scene in the novel Star wars where Vader said that he was going to arrange the company's reunion with the princess preceded one in the trash compactor. One could guess the same sequence was predetermined for ANH. Automated compaction didn't fit the logic of the imperials trying to capture or terminate them.