It was long foreseen, but when it finally happened, it still seemed spooky. The FDA last week approved an implantable microchip for medical uses. When activated by a handheld scanner, the tiny VeriChip emits, via radio signal, an ID number that can be linked to a patient's medical records. Critics see Big Brother. Enthusiasts say ambulance crews and ER doctors will be able to access such critical data as medications and drug allergies, even if a patient is unconscious. Future versions may have sensors to read vital signs like pulse, temperature and blood sugar.