You can inspect these products and see how they work at a local pool or pool fence company:
One device is the Floating Pool Alarm with remote alarm that can be heard in the house. The water needs to be disturbed for this to work, so if your child slips into the pool, he might not make a large enough splash to set off the alarm.
Another alarm type is the Infrared Alarm System which detects motion in the pool.
The third is a Removable Safety Fence usually made out of mesh. This has been proven to be an adequate safety barrier.
Survival Training for children
Teach children to roll over and float on their back. Also, instruct children, especially toddlers who can learn this to get to the side and hang on. Check with swim class instructors for the proper method.
What to do if a child is found in the pool unconscious:
Call 911
Initiate CPR
Parents can erect layers of barriers to reduce the risk of accidental drowning. Every obstruction that you place makes it that much more difficult for your child to drown. Fences, door alarms, swimming lessons all provide an element of safety.
Your local chapter of the Red Cross offers pamphlets as well as CPR and swimming classes. Fencing companies and pool companies are also good sources for safety products. But beware: Do not let yourself be lulled into a false sense of security by installing pool safety products. These are only one layer of barrier.
Remember the most important element is to supervise closely any children in a pool. Never leave children alone.