A Doo radio transmitter, officially known as a T-1151 radio transmitter, is a radio transmission device camouflaged as a pile of animal droppings or, in its most common form, a large single fecal dropping from an animal indigenous to the area of intended use. Regardless, the external form of the device was designed to discourage close examination and thus, detection or disruption.
Initially developed by United States military intelligence about 1970, the Doo transmitter was a homing device camouflaged as dog or monkey feces for use in Vietnam. At just over four inches long and three-quarters of an inch in height, this inconspicuous spy tool was small enough to be carried easily. It could send or receive radio messages, usually by Morse code. The effectively camouflaged beacon was positioned throughout the jungles of Vietnam, where it transmitted a radio signal that helped aircraft pinpoint key enemy ground sites for strikes or reconnaissance. The device often had a peat moss crusted shell.
Developed by the United States military intelligence in the 1970s, the poop transmitter was a homing beacon. Here's an x-ray view of its interior:
The museum's description:
Dropped along the Ho Chi Minh trail by air, this device transmitted a warning when supply movements occurred during the night. The signals were monitored by a variety of agencies, including the CIA.
Gale Encyclopedia of Espionage & Intelligence:
At just over four inches long and three-quarters of an inch in height, this inconspicuous spy tool was small enough to be carried easily. It could send or receive radio messages, usually by Morse code. (...) Because the Doo transmitter was often left undisturbed, operational life was often a function of the battery life of its nickel-cadmium battery array. This advantage was often essential when the transmitter was utilized as a homing device. Because the device gave the appearance of fecal matter, it was often left undisturbed and thus a retained high efficiency as a homing beacon even when planted days or weeks before a mission.
Related (sort of) spy gear:
Lipstick gun (wiki) This 4.5mm single shot weapon disguised as a tube of lipstick was referred to as The Kiss of Death. Used by KGB operatives during the Cold War, the existence of the weapon was first detected at a border crossing into West Berlin. Apparently the KGB also had a single shot Rectal Pistol which was encased in rubber and hidden exactly where the name suggests. I was unable to find a picture of it.
Paging Maxwell Smart - here's a shoe with a heel transmitter: In 1960s and 1970s , this spy gear gadget was invented by Romanian Secret Service.The shoe contained with a hidden microphone and transmitter, thus enabling Romanian Secret Service to monitor the conversations of the unsuspecting target.
Not sure if James Bond ever used these particular gadgets, but here's a wiki of everything he did use, and here are some books about spy gadgets.