Swimming pool alarms are one part of a pool barrier.
However, the volume and sound of the alarm is just as important as the device itself. Guidelines for most models say that the alarm should sound out 85 decibels at 10 feet from the device. It should also have a different sound from other alarms and should be a distinct noise.
Test out alarms with your pool safety retailer to find one that will work best for the location of your swimming pool.