Abstract: A digital swimmer safety system has a programmable radio communications device, such as a smart phone, in communication with a personal radio transmitter on a swimmer. The communications device established a digital connection with the radio transmitter and starts a timer if the signal is lost. The signal may be lost due to submergence of the transmitter in water. If the timer exceeds a threshold, then an alert is displayed. The communications device is configured to continue monitoring the swimmer in background mode so that the user of the device can run another app. The system can be configured so that multiple swimmers can be monitored by the same communications device and different threshold times can be set for each swimmer depending upon their swimming ability.