High - resolution digital cameras; wireless radio transmission; computer and master station 

High-tech cameras are installed into the pool´s walls, surveilling the activities below the water surface. The cameras are filming the action under water (frame grabbing) and all pictures (better videos) are sent in form of huge data amount to the Central Processing Unit (CPU). Here all datas are analized by a  special "intelligent" software.

The software is able to

a) detect a floating person in the water or on the pools ground
b) to recognize the period of time, the person is floating or laying on the ground motionless
c) to raise alarm to the lifeguards via wireless radio transmission once the person seems to be in danger (drowning)
d) to inform the lifeguard about the exact area, where the person in danger is located (important specially in a pool of bigger dimensions)

Apart from wireless radio transmission sets for the lifeguards (which enable the lifeguards also to communicate with each other) a separat workstation can be mounted. Then the lifeguard can oversee the water surface once he is not actually near the pool but in his office.