An inertia igniter including: a housing; and a movable striker supported by first and second stages, the first stage having a first locking element for releasing the second stage upon a first predetermined acceleration of the housing and the second stage having a second locking element for releasing the striker upon a second predetermined acceleration of the housing greater than the first predetermined acceleration. Wherein the first and second locking elements of the first and second stages occupy a common cross-sectional volume along a longitudinal axis of the housing.