A switch assembly (17, 24, 56, 200) for use downhole, comprising: an outer cylindrical housing having a common axis and a thru bore; an electrically insulating inner cylindrical housing located within the thru bore of the outer cylindrical housing having a thru bore; a cylindrical electrically conductive receptacle having a thru bore and located within the thru bore of the inner cylindrical housing; an electrically conductive piston with a first end having a conical cavity, a distal end, and a circumferential groove about the distal end; an electrically insulating piston sleeve surrounding the circumference of the first end of the piston; an axially slidable electrically conductive firing pin having a first cylindrical segment, a second intermediate cylindrical segment, and a third cylindrical segment, wherein the first cylindrical segment is axially slidably engaged with the thru bore of the receptacle and covered in an electrically non-conductive material, the second cylindrical segment is axially slidably engaged with the thru bore of the inner cylindrical housing, the third cylindrical segment having a conical distal end located adjacent to the conical cavity of the piston; a first wire electrically coupled to the first segment and a second wire electrically coupled to the receptacle; an electrically insulating bushing (210; 300) with a base end (220; 301), a cylindrical sleeve (221; 302), a distal end, and an thru bore, wherein the thru bore of the bushing is slideably engaged with the distal end of the piston; wherein, in a first piston position, the circumferential groove of the distal end of the piston extends beyond the distal end of the bushing (210; 300) and the second cylindrical segment is out of the receptacle; wherein the base end (220; 301) of the bushing (210; 300) is proximate to the piston sleeve; wherein the bushing (210; 300) in combination with one of an o-ring in the circumferential groove of the distal end of the piston, a retainer ring in the circumferential groove of the distal end of the piston and a shear pin in the circumferential groove of the distal end of the piston restrains the piston in the first position; and wherein, upon detonating of a shaped charge (13, 20, 47, 63), an explosive force causes the shearing of the one of the o-ring, retainer ring, and shear pin against the bushing, and an axial movement of the piston from the first piston position brings the second cylindrical segment into contact with the receptacle. an outer cylindrical housing having a common axis and a thru bore; an electrically insulating inner cylindrical housing located within the thru bore of the outer cylindrical housing having a thru bore; a cylindrical electrically conductive receptacle having a thru bore and located within the thru bore of the inner cylindrical housing; an electrically conductive piston with a first end having a conical cavity, a distal end, and a circumferential groove about the distal end; an electrically insulating piston sleeve surrounding the circumference of the first end of the piston; an axially slidable electrically conductive firing pin having a first cylindrical segment, a second intermediate cylindrical segment, and a third cylindrical segment, wherein the first cylindrical segment is axially slidably engaged with the thru bore of the receptacle and covered in an electrically non-conductive material, the second cylindrical segment is axially slidably engaged with the thru bore of the inner cylindrical housing, the third cylindrical segment having a conical distal end located adjacent to the conical cavity of the piston; a first wire electrically coupled to the first segment and a second wire electrically coupled to the receptacle; an electrically insulating bushing (210; 300) with a base end (220; 301), a cylindrical sleeve (221; 302), a distal end, and an thru bore, wherein the thru bore of the bushing is slideably engaged with the distal end of the piston; wherein, in a first piston position, the circumferential groove of the distal end of the piston extends beyond the distal end of the bushing (210; 300) and the second cylindrical segment is out of the receptacle; wherein the base end (220; 301) of the bushing (210; 300) is proximate to the piston sleeve; wherein the bushing (210; 300) in combination with one of an o-ring in the circumferential groove of the distal end of the piston, a retainer ring in the circumferential groove of the distal end of the piston and a shear pin in the circumferential groove of the distal end of the piston restrains the piston in the first position; and wherein, upon detonating of a shaped charge (13, 20, 47, 63), an explosive force causes the shearing of the one of the o-ring, retainer ring, and shear pin against the bushing, and an axial movement of the piston from the first piston position brings the second cylindrical segment into contact with the receptacle.