In the Shadowrun universe, a cranial bomb is hunk of explosive material connected to a cyberware interface which dictates if, when and how the explosive will be detonated. All of this technology is then inserted into some poor sap's skull, either with or without his permission. There are actually three types of cranial bombs, varying in power which can be tailored to the application at hand:
  • Kink bombs: These are what people think of when they hear the words "cranial bomb." They consist of a small amount of explosive placed adjacent to the cortex of the victim and their only application is to kill the carrier. The amount of explosive is small enough that it will not injure bystanders. In fact, you won't even hear a kink bomb unless it's inside your head. The bomb can also be placed near or within implanted memory cyberware and be used to destroy it, leaving the carrier unharmed or with only minor physiological defects such as stuttering or blindness.
  • Microbombs: The microbomb is just powerful enough to kill the carrier. In fact, this is its only purpose. The microbomb, when detonated, will instantly kill the bearer and will probably shower those near him in a gray matter paste.
  • Area bombs: Nick named the "cranial nuke" on the streets, this bomb is a hunk of plastic explosive big enough to have a blast radius. It will certainly kill the bearer, turning his head into a swirling mass of blood and skull. The bomb is also capable of killing anyone standing near him. The effective radius is dependent upon how much and what type of explosive is rigged in the poor sucker's skull.
These bombs can all be rigged using standard means such as a timer or a remote radio detonator. Some have been tricked out to use a voice password, picked up by the victims ear's and decoded by the bomb cyberware, thus triggering the explosive. There have been nasty stories of rogue radio signals in the sprawl tube system triggering random explosions, and often killing several people who were unfortunate enough to be in the same car as the kinked bomb carrier.

Cybertechnology: A Shadowrun Sourcebook by Tom Dowd