a device for terminating the flow of fire - extinguishing fluid from an activated sprinkler head of the pendent and sidewall types . a cavity within the device receives the sprinkler head and a protuberance within said cavity engages the valve assembly and returns the shut - off valve to the fluid - emitting conduit . biased apertures within the sidewalls engage the sprinkler head flange and provide a locking means . the device is constructed from thermoplastic resins which melt and allow the device to become reactivated when ambient temperatures reach critical levels .