To pick out potential drowning victims，anyone in the water who starts to descend slowly is added to the software’s“pre．a(chǎn)lert”‘list．says McQuade．Swimmers who then stay immobile 011 the pool bottom for 5 seconds or more are considered in danger of drowning．Poseidon double·checks that tell image really is of a swimmer ,not a shadow．by seeing whether it obscures the pool’s floor texture when viewed from overhead．If SO，it alerts the lifeguard。showing the swimmer’s location on a poolside screen．The first full．scale Poseidon system will be officially opened next week at a pool in High Wycombe ，Buckinghamshire．One man who is impressed with the idea is Traver Baylis，inventor of the clockwork radio．Baylis runs a company that installs swimming pools—and he was once an underwater escapologist with a circus．”I say full marks to them if this works and can save lives，