A body implant transmitter with a coil antenna is surgically implanted into the peritoneal cavity of a mammal and allowed to float freely. This design is commonly used on mammals whose neck circumference is greater than their head circumference and neck collars are not appropriate. A high degree of skill is required to surgically implant the transmitter and there is risk of infection. Field range is reduced due to the coiled antenna and body mass of the mammal.

Series	Weight (grams)	Life (days)	Description
M1200	13.0-145.0	211-5575	cylindrical shape, extended range option available.
M4100	460	2816-3896	Mammal Rumen Implant, extended range option included.