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I see browsing the site that in the past there has been some confusion about the usefulness of 121.5 MHz ELT emergency beacon freq. A few months ago I went on a ground search for a 406 MHz emergency beacon. It turned out to be inadvertent triggering and all was well in this case. But I can tell you from this and other experience that if we did not have the homing ability of the 121.5 MHz companion signal from the 406 MHz equipment the ELT battery may have run dead on the unit before we ever found it. We were given Lat, Lon coordinates by SAR derived from a 406 MHz ELT beacon transmission to start the search. But we actually found it 3 miles away (typical). As a side note, CAP aircraft are equipped for 121.5 MHz homing but were not used in this search. PLB's and EPIRB's I believe transmit on both 406 and the 121.5 MHz frequency when triggered also. My observations from this type search 1) The 121.5 MHz is monitored by many commercial and some of us GA types while flying. We often still get reports of 121.5 triggering from these sources and was verified by commercial aircraft on this occasion also. 2) We get a very small search area IF your 406 MHz ELT has the ability to output a GPS signal to SARSAT. Typically within a few hundred meters, but not all 406 MHz ELT's have this ability! 406 MHz ELT's without the GPS output ability have a much larger search area. Our target in this case did not have GPS output thus a longer search time to find it. 3) In heavy ground or wooded cover the 121.5 may be the only reason SAR will find you. Especially for PLB's. 4) Our search area had mostly cell coverage but in many areas there was none especially in the low areas of the hilly terrain. Cell phone may or may not be a good backup but there are lots of recreational places in our state where coverage is nil. 5) If you have one of these devices, a 406 ELT or PLB or EPIRB, registration rules for the device's need to be followed to protect us all. I like many don't like a bunch of additional rules but to protect us and our passengers it can be very useful in this case. My observations on 121.5 homing, I hope this helps.