Abstract: A method for detonation of a plug device in a fluid environment is described, which is in contact with a body, such as an ignition pellet, and it is characterized in that a number of pressure increases are exerted against the plug device, whereby each pressure increase causes a movement of a piston (10) which is radially arranged in a casing (12), which causes the casing (12) to move a fixed distance inward in the plug device with each pressure increase, up until the displacement of the casing (12) causes the piston to be displaced into a cavity (38), and the fluid environment enters the plug device via an inlet. Also described is a plug device which is in contact with a body, such as an ignition pellet, where the plug device is arranged to detonate after a number of pressure increases that are exerted against the plug device.