Lithium and saltwater do not mix well, some nonsense about lithium hydroxide, volitile, exothermic reactions, etc. Should someone decided to install a smoke detector under the battery cap of a PRISM, complete with lithium battery and, hypothetically (since we all know that PRISM divers *never* flood their rigs
), should the battery compartment flood, the analog secondary would back up the electronics assuming the loop is not destroyed and the diver's head is intact following the explosion.