When my daughter wore the wrist band for a year, we only took it off for a bath and it went right back on.
There are systems that work on a bouy concept. A thing floats in the water that measures anything that is 10 pounds or more stepping in and out of the water. But that also has to work only when it's in the pool. If someone gets out and forgets to throw it back in, then it's worthless.
There are also systems that work on infared concept. Devices are put at 4 corners around the pool and anyone stepping through will set off an alarm. But again it has to be on and people will shut it off when using the pool and maybe not put it back on.
In the end after looking at all the choices, I felt the wrist band was the safest. The only false alarms we had was once when she and my husbands was walking outside when the sprinklers went off and a couple times when I put her in the bath before taking it off and once when she drooled on it in her sleep. It worked well.