An apparatus actuatable under a rotary acceleration having a predetermined duration and magnitude. The apparatus including: a body having a first channel and a second channel, the second channel being disposed radially offset from the first channel; a mass disposed in the first channel, the mass having an arm disposed at a first end of the mass and the arm being rotatable from a first position in which the arm cannot move within the second channel to a second position in which the arm can move inside the second channel; a first biasing spring member having a first end connected to the body and a second end connected to the arm such that when the arm is subjected to the rotary acceleration greater than the predetermined duration and magnitude, the arm is biased to rotate from the first position to the second position; wherein the mass is connected to the arm such that the mass moves in the first channel and the arm moves in the second channel when the arm is biased into the second position.