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.

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 is somewhat like a walking tank. He makes up for the ChassisBot's weaknesses as the ChassisBot makes up for SentryBot's weaknesses, making a powerful team.