By passing of electric current it is heated to a high temperature that starts the exothermic chemical reaction of the attached composition.
Another material, able to actively release chemical energy, is Pyrofuze, aluminium wire clad with palladium; when being heated it undergoes strongly exothermic reaction as the molten metals form an alloy.
[2] Bridgewires, especially connected to longer cables, may be susceptible to initiation by currents induced by external electromagnetic fields.
[3] By passing an extremely high amount of electric current through the bridgewire, it gets rapidly vaporized, causing a small explosion.
This is exploited in exploding-bridgewire detonators (EBWs), used for very safe and highly precise initiation of explosives, e.g. in nuclear weapons.