Abstract: A fire sprinkler has a flow passage for water or other extinguishing fluid closed by a frangible body, which may be a simple disc. A separate mechanism responsive to temperature-rise conditions shatters the frangible body, and the fluid then flows from the passage to impinge on a distributor (as in conventional sprinklers). The shattering mechanism is preferably actuated by a shape-memory alloy, preferably in sheet form, which can be located below the distributor for maximum exposure to radiant as well as convective heat; it can also be thermally insulated, contributing further to speed of response.