Homer
Q Branch
Goldfinger
1964

As Q explained, the Homer was "...to be concealed in the car you're trailing while you keep out of site....audio-visual range -- 150 miles." The Homer's signals are picked up on a Receiver.

007 made quick use of this gadget by placing it in the trunk of Goldfinger's Rolls Royce Phantom 337 after their round of golf. This enabled him to trail Goldfinger to his metallurgy plant in Geneva, Switzerland, and ultimately find out the bigger scheme behind the gold smuggling.