The robot guard, also known as the defense robot, is a perimeter defense used by the Krimzon Guard in Jak II. They were first seen at the pumping station in the mission "Find pumping station valve", again seen in the Water Slums in the mission "Get seal piece at Water Slums", and lastly found at the Metal Head nest upon arrival there.
The drone is rarely visible from any other view than up front. It has a large metallic shield, colored white with red and a big blue screen for an eye. The drone is armed with two powerful blasters and possibly some other equipment which it uses to stay underwater.
Security drones stay on the bottom of the sea floor (or whichever body of water they inhabit) and will rise once the security system detects something entering the water. Once surfaced it will sound a computer voice saying one of many scripts. If the target does not return to normal ground or continues going forward the drone will shoot them. The Krimzon Guard deployed these during an ambush on Jak when he was retrieving a piece of the Seal of Mar in the Water Slums.
The security drone has one attack, after giving you a short warning, where it shoots two powerful blaster shots at you, that do not miss and instantly kill you. To avoid it, do not enter the water, although even if you do you can still retreat for a short time. At the pumping station you can go a varied distance before triggering it, although at the Metal Head nest it will instantly appear the moment you get into the water.
Normally indestructible, a Dark Bomb from Dark Jak is capable of destroying it. Rely on timing so you hit it when it surfaces, it does not have an explosion or death animation however, only a dark purple stream going far down (indicating the bot went down into the water with the dark bomb following it). Similarly you can survive its attack by turning into Dark Giant, which will leave you with a single hit point. If you manage to destroy it, Jak will be able to swim or JET-Board as far as the water will go. Going beyond the game's boundaries will mean falling through the water into a bottomless pit.