I think they do, fizz, but only triggered manually or on impact (sometimes). Even some light aircraft have them, and have had them for many years....
Must be over 10 years since Search & Rescue were puzzled by a transmitting emergency beacon in Queensland.....they couldnt locate it as it kept moving. Eventually found it in a pranged Cessna being transported on a semitrailer minus wings....someone had accidentally triggered it putting the plane on the truck. I'm sure MH370 had an Epirb, also one in each of its life rafts, on logic.
