A power source for generating electrical power. The power source including: a shaft rotatably disposed relative to a structure; an elastic element having one end attached to the shaft and another end attached to the structure for storing potential energy upon rotation of the shaft in a first angular direction; a generator operatively coupled relative to the shaft; and a retaining mechanism movable between an engaged position for retaining the shaft from rotating in a second angular direction opposite to the first angular direction and a power generating position permitting the shaft to rotate in the second angular direction. Wherein, when the retaining mechanism is moved to the power generating position, the stored potential energy in the elastic element is converted to kinetic energy to rotate the shaft which in turn rotates the generator coupled to the shaft so as to produce electrical power.