Booby traps may be designed to function as early warning devices, cause injury, or kill. Alarm type booby traps are passive devices used to warn a perpetrator that someone is approaching, to impede access during a police search or raid, or to slow or stop police pursuit of a suspect. This type of device may include hand grenade simulators, chemical agent devices, smoke producing devices, military trip flares, and perimeter alarms. Booby traps designed to maim or kill include, in addition to types that detonate or burn, boards with nails or spikes driven through them and then camouflaged or buried in a hole which is hidden from view, causing serious injury to anyone who steps on or falls onto the spikes; firearm traps, where a hidden trip wire will cause the weapon to discharge in the direction of a pursuing officer; and fragmentation devices which explode and scatter pieces of the container and/or missiles outward from the point of detonation at great velocity. The article describes booby traps as attractive to some criminals because they do not require special knowledge, sophisticated explosives, controlled components, or materials that are hard to obtain.