Sentry Turret

Sentry Turrets are the main weapon of GLaDOS. In the game, you find a turret facility place where it throws out the "crap" turrets and uses sthe ones that say "hello" in a creepy voice

but, you take out the main turret and the machine goes by memory, but eventually you save a crap turret and make IT the main turret. which makes GLaDOS' turrets CRAPPY.

Defective turrets
These ones say funny things like:

"Hey, squeaky voice, got any bullets?"

"Put me in the game, coach!"

They seem to have no plating and no... eye? they also are probably just mistakes.

They have no ammunition for a weird reason.

But they're not bad.

"good" turrets
These ones say stuff like:

"Hello."

"Search Mode Activated!" (after they see Chell and she goes out of sight)

"Target Spotted!" (When they see Chell)

"Critical Error" (Before they die)

They have squeaky voices and are dangerous to the player