An inertial igniter for use with a thermal battery for producing power upon acceleration is provided. The inertial igniter including: a base; at least one member disposed on the base, the at least one member having a hole; a mass movable towards the base, the mass having a concave portion; a locking ball disposed in the hole in the at least one member and having a portion thereof disposed in the concave portion for preventing relative movement of the mass with the base when an acceleration time profile is below a predetermined threshold; and a biasing spring including a portion for preventing the locking ball from leaving the concave portion when the acceleration time profile is below the predetermined threshold and for allowing the locking ball to leave the concave portion when the acceleration time profile is below the predetermined threshold to unlock the mass and permit movement of the mass relative to the base.