Abstract: In a reserve battery initiator a unitary moulded ampoule (10) containing an electrolyte comprises two portions conjoined by a mechanically weak section (11). The ampoule (10) may be ruptured by a striker (3) which is released when the initiator is subjected to sufficient an accelerative force to overcome a detent mechanism. The ampoule may also contain an insert (12) to transmit to the weak section the force imparted by the striker. The insert (12) may additionally have a cutting effect on the weak section (11). Conveniently the insert is in the form of a frustrum with a narrow end contiguous with the inner face of the ampoule at the location where the striker (3) impacts and a wide end contiguous with the inner face of the weak section (11).