When a PLB or an EPIRB transmit they send their signal up to the COSPAS-SARSAT network of satellites that process the signal and provide a location which is then sent downstream to ground station local user terminal known as a GEOLUTs.
The main GEOSAR satellite for our area is MSG-2 which has GEOLUT terminals located in Algiers, Toulouse, Pentelli (Greece), Bari (Italy), Fauske (Norway), Spain, Ankara and Combe Martin (UK). The GEOSAR network only processes signals from devices with GPS information as they are Geostationary satellites and therefore don't use doppler shifts, whereas the low earth orbiting LEOSAR network processes 406MHz signals with no embedded GPS co-ordinates and rely on multiple satellites to pass over you to narrow down your position via doppler shifts.
The GEOLUT's then send the information to a Mission Control Center who in turn forward the distress to the nearest rescue co-ordination center (in our case RCC Malta), who come out and get you!
It's important to stress that one of the main advantages of an EPIRB over an PLB is that it gets it's optimum signal when floating, whereas a PLB needs to be held above the water with the aerial pointing skywards and nothing covering the GPS receiver area. If you're unconscious or something like that you'll get a reduced or no signal as the PLB can't be held, whereas if an EPIRB auto deployed it would be floating and transmitting in the clear so to speak.http://www.cospas-sarsat.org/Description/leosarSystem.htmhttp://www.cospas-sarsat.org/Description/geosarSystem.htm
MacMurdo Fast Find Max will set you back ?239 incl VAT and has a 121.5MHz homing signal beacon as well but no GPS.
MacMurdo Fast Find Max G +GPS will set you back around ?350 incl VAT and has a 121.5MHz homing signal beacon as well
MacMurdo Smartfind E5 EPIRB Manual (No GPS) - ?299 incl VAT
MacMurdo Smartfind E5 + GPS EPIRB Manual - ?449 incl VAT
ACR units are a bit more expensive but considered to be top-notch.