STI-1100 STI Stopper Ii W/Horn Flush MountSTI STI 1100 Stopper II Flush Sounder Larger cover helps prevent malicious or accidental false fire alarms. The Stopper II is a unique device which has helped prevent false fire alarms around the world for more than 30 years, without restricting legitimate operation of devices such as fire alarm break glass call points. It is ideal for schools, colleges, hospitals, nursing homes, hotels and all public buildings where there is a history or a threat of