Galvanic chemistry oxygen sensors used in rebreathers and diving gas analyzers are all based on using a metallic lead anode in potassium hydroxide liquid electrolyte, and also contain a miniscule amount of pure gold used with electrical connectors. Potassium hydroxide (aka "potash") is a caustic alkaline chemical which can require special handling; do not break open the plastic housing of the sensor. We suggest following the same rules your locality would have for disposal of ordinary consumer grade alkaline or lead-acid batteries. Galvanic chemistry oxygen sensors are also considered recyclable electronics for their metals.