A Personal Data Transmitter (PDT) is a form of personal locator typically surgically implanted into the body of extrasolar colonists, among others. Its purpose is to allow rapid location of the associated personnel anywhere within a certain radius of the receiving equipment, sometimes up to 30km distance. They are also capable of relaying rudimentary vital signs regarding the user, although this particular function is known to be subject to malfunction.
The colonists at Hadley's Hope on LV-426 all had PDTs implanted as soon as they arrived on the moon. Colonial Marines were also equipped with PDTs, contained within their M10 Pattern Ballistic Helmets.