The Thelma Biotel transmitters are energy efficient and versatile platforms developed for a wide range of studies on aquatic species and submerged equipment. The various transmitters are produced in five main transmitter diameters: 6mm, 7 mm, 9 mm, 13 mm, and 16 mm. Transmitter lengths depend on the possible addition of sensors, output power and the desired active lifetime.

In addition to the range of standardized, off-the shelf products, the transmitters are highly customizable in both hardware and software. The sensors available are depth, temperature, acceleration (activity), inclination (tilt angle), mortality (tilt angle), conductivity in fresh water and salinity in salt or brackish water. All sensor combinations are available down to the smallest size of 6, except for the conductivity and salinity products which have a minimumsize of 9 . The transmitters can be programmed to utilize any carrying frequency between 63-77 kHz, and at any transmitting interval. For fish studies and equipment compatibility, 69 kHz is most commonly used.