I purchased this alarm about a month ago and thought I would post my review.
The unit is fairly easy to install, just drill a hole in your concrete, insert a 9v battery and stick it in the pool. That's about all there is to the install. The unit seems to work fairly well. It is activated by the amount of waves (I think) in the pool. I tested it by sliding a couple of full bleach bottles into the pool, and though it took about 10 seconds, the alarm did trigger. Granted if I jump into the pool the alarm will sound almost immediately.
I have yet to have a false alarm, but we haven't had any real large storms this past month. Hard rain doesn't seem to set it off by itself, I would guess you would need some wind to get the surface of the water moving.
Now for the cons: The unit alarm is well designed, but the controls leave something to be desired. The unit can not be turned off. I suppose this is to prevent a child from deactivating the alarm. However this makes removing and reinstalling it difficult without setting the very loud alarm off. The unit does let you hold the "sleep" button in for 3 seconds which supposedly gives you a window where you can remove or install the alarm without activating it. I am successful at removing it about 50% of the time without the alarm going off (my wife is about 10%, grrrrr). Reinserting the unit is even worse. It is almost impossible to get the stabilizing rod into the hole and the unit in the water without sounding the alarm. This is not a huge deal, but some better controls would make a world of difference. I really think my neighbors are getting tired of me setting my alarm off.
The unit also comes with a remote alarm that seems to work fine although we have not used this much. You just plug it in wherever you want and it sounds when the units sounds.
Another control that would be nice and is lacking is a way to turn the alarm off remotely. If we were ever to get a false alarm in the middle of the night we would have to go out to the unit to disengage the alarm. It would be nice to be able to point a FOB out the window to turn it off.
All in all, it is good unit that does what it is supposed to do (and no more). If you have young children in the house it definitely gives you an added level of insurance and a little more peace of mind.