The bio-sensor is a small Tok'ra device which was used to monitor every aspect of an individual's physiology. It was worn on the chest of the individual and could transmit its data wirelessly over long range distances to a display device.
The device was circular in shape and flashed lights colored red, white, blue and yellow. (SG1: "Upgrades")
History
Dr. Janet Fraiser places a Tok'ra bio-sensor on Daniel Jackson.
In the year 2000, Anise had Colonel Jack O'Neill, Major Sam Carter and Dr. Daniel Jackson wear the bio-sensors when they tested the Atanik armbands. They were able to detect the traces of an antibody to the virus that allowed the armbands to enhance their wearer's speed and strength. (SG1: "Upgrades")
References
- GateWorld's article on Tok'ra bio-sensor in The Stargate Omnipedia