Some pool stores sell an alarm that attaches to a child's arm like a wristwatch. It sounds an alert when submerged. Two kinds of nets are made to cover the surface of the water. One is mostly used in the North, to close pools for the winter. It is a tightly woven cover that pulls over the pool.
Some newer nets resemble a cargo net, with four-inch squares.
Kids could still reach through it and touch the water. Some pool suppliers say a kid could get tangled in it, or still reach the water.