If you have a small child and a swimming pool, then it's at least a little likely that you may sometimes worry about said child falling into said pool. Well, it was with that concern in mind that British electrical engineer John Barstead created the Dolphin Alarm.

Here's 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.

Barstead and his team are currently raising production funds for the Dolphin Alarm, on Kickstarter. A pledge of £143 (about US$201) – which is 50 percent of the planned retail price –will get you a system, when and if it reaches production.

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