British electrical engineer John Barstead created a sonar alarm system that will warn parents or nearby sunbathers if a small child has accidentally fallen into a pool. The Dolphin Alarm, as it is called, is currently raising production funds on Kickstarter. New Atlas explains how it works: When small children who have no business going into the pool on their own are out playing near it, they wear a special wristband. If they should fall in, the wristband will generate a three-tone sonar signal as soon as it’s immersed in the water. That signal will be detected by a hydrophone contained within a receiver unit that floats in the pool. When that happens, the unit will emit a 131-decibel alarm. It will also transmit an alert to an indoor remote unit located up to 150 m away (170 ft), which will likewise sound an alarm of its own. While there are other child-in-the-pool alarms, most of them are wave-activated and have to be shut off when other people are using the pool.

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Source: Slashdot – Engineer Develops Sonar Alarm System To Monitor Kids In the Pool