The Sentinel Droid was designed for the purpose of maintaining security and apprehending lawbreakers. Based on ancient human replica droid technology, it was created to replace living soldiers, guards and other security personnel. The design is now antiquated and has been replaced with more capable and efficient droid designs; though at the time of production the Sentinel droid was the epitome of military droid technology.
Distinctive production features of the Sentinel droid included a light blaster rifle, which it could fire with uncanny precision, enhanced optics, allowing it to identify and track enemies or criminals easily, and basic weapon skills. This combination of features allowed the Sentinel droid the capabilities to serve as front-line soldiers, bodyguards, security personnel, bounty hunters or even as assassins. Though the Sentinel droid lacks the sophisticated programming of much deadlier assassin models and the domestic capabilities of protocol droids, they could be deployed en masse to overwhelm enemies with sheer numbers.
Being unique in function at the time of its release, the Sentinel line of droids created a new market for military and security forces. It made available a soldier that did not require sleep, food or training and was always on guard; basic maintenance would allow the droid a long operational life that would easily exceed the longevity of any of their organic counterparts.
Nearly four millennia ago the Sentinel droid saw first widespread use when it was deployed during a time of war. Both the Galactic Republic and the Sith used them in the capacity of front-line soldiers and the Republic would continue use them as security forces for many years after. It was considered the most advanced mass produced military model droid during this time period, but the Sentinel droid is now considered long past its prime. Most existing models can be found as deactivated exhibits in museums and personal antique collections, however they are infrequently used in an active capacity in the outlying areas of the galaxy; where modern security droids are too expensive or cannot be obtained.