These are Primarily MULTI POWER MULTI FREQUENCY DISTRESS BEACONS controlled by a nano power Atmel or PIC controller. various Tx are switched on automatically at a fixed interval based on a RTC. The blips are detected by directional Rx working on diff freq. Last leg is based on BLE beacon having upto 100m range and an android mobile can be used to zero in on the casualty. The Costs given are only indicative of a hobby project.