The main difference between an EPIRB and a PLB is that EPIRBs are designed to signal maritime distress, while PLBs were originally designed for land-based applications. A traditional EPIRB is mounted to your vessel, and will generate a distress signal automatically if immersed in water, if it is a
Category I EPIRB, or when you manually flip the switch, if it is a
Category II EPIRB. They are mandatory on commercial vessels, and are becoming increasingly popular as personal EPIRBs become available and more affordable. Historically, PLBs are portable units that operate much the same as EPIRBs, but they are designed to be carried by an individual person instead of on a boat. Many boaters are using this type of emergency locator beacon rather than an EPIRB. PLBs can only be activated manually, which is a significant factor to consider when deciding to buy an EPIRB or a PLB.
When determining which emergency beacon to purchase, keep in mind that some type of beacon is better than nothing. It's not a "should I buy" scenario, but a "which one should I buy?" because every boater should have either an EPIRB or a PLB. In some cases, it's not a bad idea to have both. Boats sink or capsize and people fall overboard even with the best planning, boating skill and experience in the world.
Hope this helps..