The triggers for "Spencer" in Impostor (2001)

This was written in reply to a comment under a YouTube movie recap.

After the hospital scan, the main agent knew with definite evidence, that Spencer was a planted robot with a bomb inside his body. Whether there was prior knowledge of his wife, is unknown.

The greater plan for humans must have been to move the married couple away from populated areas, which would defeat the aliens' big plan, though they did get some solace in the knowledge, that the entire ruse managed to decimate the robot-detecting operation. — This explains, why the agents are inadequate or inexperienced, in that similar explosions have happened before, and there's a manpower problem.

The film is clever, in that Spencer's detonation trigger was actual definite knowledge of being a robot. On second viewing, we see how close he is to learning of his botness and his body detonating, but the aliens did not account for Spencer's humanity even as a bot.

There may be differing accounts as to what other things may have triggered Spencer and his bot "wife". It could be, that both the "husband" and "wife" had to be in close proximity, and Spencer's earlier refusal to acknowledge his botness must have been due to the absence of his "wife".

We must assume very sophisticated programming: Spencer's AI mind learns, that he's about to be exposed, but he cannot yet trigger his internal explosive unless and until he's relatively close to his "wife", which "subconsciously" causes him to escape and seek his wife in order to prevent the bomb from being safely removed from either unit for reverse engineering, and to complete the mission to minimise exposure.

The movie shows a setting, where humans are able to make a stand, but are always one or two steps behind.