To add to above comments for more clarification. The sentinel can actually insta-kill teammates with full health/armor under specific conditions which are: The sentinel has to first be in recharge mode or down (when showing red after it's firing animation is concluded), then if a player is standing directly underneath or within the radius of the Sentinel's immediate vicinity, once a Zed gets close it will trigger the Sentinel's auto self destruct which in turn kills the player instantly. The kill meter then displays the player death as if it was a self inflicted death.