A GFCI outlet watches the current going out on one wire and coming back on the other. If even a few milliamps go missing, which is what happens when electricity finds a path through a person, it trips in a fraction of a second. It is the single most effective safety device in a home, and it costs about as much as a nice lunch.
Under the current Florida Building Code, which follows the National Electrical Code, GFCI protection is required for every receptacle in bathrooms, within six feet of any sink, on kitchen countertops, in garages and unfinished basements, in laundry areas, in crawl spaces, and anywhere outdoors. Newer editions add dishwashers, and 250-volt receptacles for ranges and dryers in some locations.
Older homes in Hialeah, Miami, and Hollywood were built under none of those rules, and that is where buyers and insurers run into trouble. A four-point inspection or a home inspection will flag unprotected kitchen and bathroom outlets, and some insurers will not bind a policy until they are corrected.
The fix is straightforward. In most cases a GFCI outlet at the first position on the circuit protects everything downstream, so a kitchen might need two or three devices rather than ten. Where the wiring has no ground, a GFCI is also the code-approved way to install three-prong outlets safely. A half-day visit usually brings a whole house into compliance.