To be honest I don't know an awfull lot about epirbs but from what I've learn't they are bringing in a new frequency so if you were to buy one you would need to look into it carefully . You can even get on on a watch .
The old style, 121.5MHz, while still currently functional, is no longer considered to fall within the requirements of a vessels safety something or other, it will be turned off in 122 days (1st feb 09) (If you have a 121.5 MHz EPIRB after this date it is nothing more than a curious pool toy or interesting coffee table deco)
in my state of my country (NSW, Australia), it is officially off the books - some states and countries maybe further ahead or further behind depending on the mood of the local lawmakers.
406 is the new frequency, and required on all vessels X metres in length going more than X miles offshore.
An epirb has certain requirements - it must be self-righting in the water with an aerial set up so if you're blacked out etc you will still be locatable, and it has to have a 48 hour battery.
the alternative, a "personal locator beacon" still uses the 406 frequency, but does not have the same self-righting, auto-broadcasting, 48-hour battery requirements as an EPIRB - these are mostly used by Bushwalkers etc in case they get lost.
an epirb or PLB ranges from 300-1000 bucks (Australian), depending on your brand, added features, and whatnot.
Be careful when purchasing EPIRBs - some sellers mistakingly sell PLBs as EPIRBS, not knowing the legislative differences, and (in my country at least) only some brands are "Approved" for whatever reasons.
If you bushwalking/hiking etc, you will be looking for a PLB, as they are generally much smaller and lighter (but not cheaper)
