Pool Safety System by Poseidon

The Poseidon Safety system uses overhead and underwater cameras to track motion and people in the pool.  When the system detects a swimmer in distress, or worse, a drowning person at the bottom of the pool, an alarm sounds and lifeguards (or parents) can be alerted with lights, alarms, alerts, or other mechanisms.

This would also be good for any pool owner to monitor activity, should a neighbour or animal fall in the pool when it's not expected to be in use.