Patent ID: 8248250

Claim:
A personal water safety device, comprising: at least three base stations arranged around a body of water in a triangle; at least one water sensing device, each of the at least one water sensing device being worn by a swimmer and wirelessly communicating with each of the at least three base stations, and each of the at least one water sensing device operable to measure elapsed time when the water sensing device is triggered after the swimmer submerges in the water, and transmit the measured time to each of the at least three base stations at a regular interval, and each of the three base stations receiving the measured time of the at least one water sensing device in different signal intensities based on a transmitting direction of time signal of the measured time; wherein the water sensing device is triggered to measure the elapsed time when an electrical conductivity of the water sensing device is in a predetermined range, and stops timing when the electrical conductivity is out of the predetermined range; an alarm apparatus wirelessly communicating with each of the at least three base stations, and operable to receive the measured time transmitted from each of the at least three base stations, and generate an alarm upon a condition that the measured time of one of the at least water sensing device exceeds a predetermined time limit; and the alarm apparatus comprising a positioning module that estimates a position of each of the water sensing device according to the signal intensities of the measured time of each of the at least one water sensing device, and positions each of the water sensing device utilizing trigonometry.