Peter's transmitter sends out signals for eight hours, and then is off for 24 hours. The PTTs have salt-water switches, which prevents the emission of signals when birds are underwater. This saves battery power so that the instruments will transmit over a longer period. Satellites need to pick up at least two messages from the same instrument on an overpass to provide a valid location. When at least four messages are obtained the location of the bird can be fixed as accurately as 150 m, but possibly only to the nearest km.
Fewer messages result in a less accurate fix.
The satellites store information, and then later on download it to the Argos data collection system in France, after which the positions of birds are accessed on line by technicians at Marine and Coastal Management, who email the data to the Avian Demography Unit, so that the SAPmap can be updated. This information proved useful in determining the likelihood of penguins at Robben and Dassen Islands being oiled during the Treasure oil spill. 2000 A transmitter is being fitten onto the back of Pamela.