PLBs are meant to assist SAR personnel to find you. EPIRBs are meant to assist SAR personnel to find your boat or your liferaft.
I think what you mean are "self-rescue" systems whereby you have a short-range locator beacon on which a shipboard direction finder can zero in:
Man Over Board Systems, MOB Rescue System, Self Managed Rescue System
The trouble is that these stand-alone systems are really expensive, and the situations in which a sailboat can effectively self-rescue a crew are typically few. Picture a cruising couple on a downwind run in a gale. A preventer line parts, the boom crash gybes, and the PFD-wearing...but untethered...husband is knocked in the head and right over the lifelines. The beacon is activated hydrostatically, and the husband's PFD also inflates.
Now you've got a guy in 20-foot waves with a head laceration, perhaps a cracked skull, very dazed or totally unconscious, in the water. He isn't sinking, but he isn't swimming, either, nor can he more than reflexively keep his head out of the water and the breaking spray, so he might drown in his PFD anyway.
The wife is hypothetically a great sailor in her own right, but she has to bring the boat around in a gale and sail or more likely motor directly into the wind in very challenging conditions.
Then what? Motoring in heavy seas next to an unconscious floater is a good way to kill him off entirely through blunt force on the hull or by beheading him with the prop. This is assuming you can even get close to keep him in sight...I hope that PFD has a strobe! Or that it isn't blackest night...
My point is that finding someone, even someone uninjured and conscious
, is no guarantee of getting them aboard a sailboat in heavy weather. Few autopilots are going to work in such conditions, and the boat itself becomes very dangerous.
If the water temperature allows it and one is coastal, the odds are better to let SAR handle it, in my opinion, but I believe the best option is to tether on religiously in any situation in which you are unlikely to have another crew save you
. That means "much of the time on passage", unless motoring through a calm.
Airbags didn't replace
seatbelts, nor do they permit terrible driving. If you work from the baseline that falling off a moving boat is a potential death sentence in every instance, you may invest less in "spot the corpse" technologies and more in behaviour modification on deck.