A stun grenade is an explosive device that emits a blinding flash of light and loud sound, designed to disorient the user's attacker or attackers.
After Helen Cutter escapes to the future, Connor Temple, Abby Maitland, and Danny Quinn prepared to follow her through an anomaly. Before the trio disembarked, Captain Becker gave Danny a backpack full of gear, as well as his shotgun. He also hands the group a stun grenade, which he believes can be used as a powerful sonic weapon against Future Predators. Becker tells them how to use the weapon, and advises them not to keep their mouths closed when it goes off, as the resulting shockwave could cause some damage. They then travelled through the anomaly, and confronted Helen Cutter in the future. They manage to escape from a pack of Future Predators without using the grenade, and end up in the Cretaceous period. The group comes under attack from a group of juvenile Raptors, and the three of them have to take refuge in a tree. Connor remembers that they still have the stun grenade available for use, and Danny throws it down to the Raptors. It goes off, and in doing so, incapacitates the Raptors. However, it also does a number on Connor, who forgot to keep his mouth shut when the grenade exploded.