The siren system we have for lightning prediction and detection is made by a company called Thor Guard. Most systems are only lightning detection systems which will detect electromagnetic disturbances in the scanned area and sound the alarm only after lightning has already struck. The same is true for sounding the all clear. Normally systems that are detection based must wait for 30 minutes since the last disturbance to give the all clear horn.
Thor Guard systems, the one we have here at WCCC, actually predicts lightning before it strikes. According to the Thor Guard website, its equipment measures the electrostatic forces that are building between the thundercloud and earth below and can predict when this field, which is capable of producing lighting, enters the zone of which you are monitoring. This being said, it uses the same technology to predict when it is safe for people to resume their outdoor activities with the least amount of time wasted sitting around and it automatically sounds the alarm.
All that being said, the answer to the question of when anyone at the club will sound the all clear is up to the technology in our system keeping us safe rather than to any one person at the club blowing a horn.
