From The TimeSplitters Wiki

SentryBot
Unlocked by	Amateur League > It's a Blast > Night Shift
Species	Robot
Size	Large
Accuracy	8
Agility	2
Stamina	10
Fire Proof	N/A
Shock Proof	N/A
Default AI	4
Native TimeZone	2315
First Appearance	TS2 Story Mode
Relations	ChassisBot The Machinist
Games	TS2

TS1 Gesture	N/A	TSFP Gesture	N/A
TS2 Gallery	Adapted from old security robots by the Machinist, the SentryBots are programmed to kill anything that moves.	TSFP Gallery	N/A

SentryBot appeared in TimeSplitters 2. He is a large character with slow agility and high stamina. In Robot Factory, the SentryBot becomes much slower and is much harder to kill than in arcade mode. The SentryBot typically requires a couple homing rockets or charge Lasergun shots to kill in Story mode. Many people use the laser/turret strategy to defeat him in story mode. This is done by having a SentryBot follow you into the level where the laser on the wall moves back and forth and lets the SentryBot get destroyed by the laser. For the second part of the level, luring the SentryBot into the range of a controlled turret is generally used to get past the SentryBots unscathed. This strategy takes a while, but is generally the easiest way to get past the level.

SentryBot appears immune to headshots, despite shooting at his apparent head section. He is a robot designed by the Machinist to help with security. He makes up for the ChassisBot's weaknesses as the ChassisBot makes up for SentryBot's weaknesses, making a powerful team.