From previous answer: "1. Even without the GPS the beacon uses a secondary 121.5 MHz frequency and will pinpoint you to within 2.3 nautical miles. Where the with GPS it is accurate to 110 yards."Correction about the above statement: As of Feb 01 2009 the Search and Rescue (SAR) Satellites will no longer monitor the 121.5MHz frequency. Only the 406MHz frequency will be monitored. This being said, the LEOSAR satellites can still determine your position with the 406MHz frequency via Doppler Shift even without GPS data. HOWEVER, the position obtained through Doppler Shift is nowhere near as precise as GPS positioning so you REALLY want to have GPS. This will narrow down the search range and make it easier/faster to find you. Furthermore, determining your position via Doppler Shift takes longer as you need to wait for one of the LEOSAR satellites to fly over you. With GPS the signal is picked up by the GEOSAR satellites which cover most of the globe, with the exception of polar regions (See http://www.cospas-sarsat.org/Status/geoCov.htm ), at all times. All the more reason to buy a unit with GPS on board. See:http://www.cospas-sarsat.org/FirstPage/121.5PhaseOut.htm for more details. The 121.5 MHz frequency will still be used as a SAR homing frequency. SAR planes and helicopters are equipped with 121.5 MHz receivers and will use that signal to pinpoint your location once they are close. Beacons MUST be registered. This is so the SAR authorities can call your emergency contacts to ensure the beacon activation is not a false alert. Beacons can be registered for free at: www.beaconregistration.noaa.gov/ for the USAwww.beacons.nss.gc.ca for Canadaor by mail or fax.If size/portability are an issue the ACR MicroFix 406 is the smallest unit. That's the one I am considering getting. Hope this helps. Play safe.