First Alert Pool Alarm
Swimming pools can be the most dangerous part of summer—about 300 children under the age of five drown in them every year. First Alert Pool Alarm is the easiest and most effective defense. Other wireless alarms detect water displacement, but the First Alert uses a much more sensitive sonar detector. A hydrophone dips beneath the water line, where it listens for sound waves within 1,600 square feet. The alarm's algorithm can distinguish between a child falling into the water and an errant pool toy, and when the system senses the former, an 85-decibel alert quickly gets the attention of adults inside the house. $700.