How long can I store the sensors?

This is really dependent on the specific sensor as each may have a different storage life.  For a general rule, we like to store our acid electrolyte sensors for a maximum of 3 months (for use with CO2 or Natural Gas).  For our standard trace sensors, they can easily sit on a shelf up to 12 months as they are packaged in a nitrogen purged bags.  For some of the higher output percent sensors, we would recommend 6 months or less.  For our long life percent sensors, 12 months.  When it doubt, reference the specification sheet of the sensor you are using as that has a more definitive answer.