Pool alarms get pitched as a safety must-have, and they're a reasonable extra layer, but "extra layer" is the key phrase. None of them replace supervision, and each type has a real gap worth understanding before you rely on one.
These detect disturbance on the water's surface and sound an alert. They work reasonably well for a sudden fall into the pool, but they can be slow to trigger for a quiet entry, and they obviously do nothing if a child is already in the water unsupervised.
These catch a child leaving the house or yard toward the pool, which is often the actual failure point in home drowning incidents. Not a lapse of watching a child already swimming, but not realizing a child left the house at all. This is arguably the highest-value alarm type for most homes.
A wristband that alerts if submerged too long. Useful, but battery and range issues are real. They need to actually be charged and worn every time, which is where they most often fail in practice.
Layer two or three of these with a proper fence and active supervision, and you've got a genuinely solid setup. Rely on any single one alone, and there's a gap somewhere.
Alarms help. Confident swimming and real supervision help more.
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