Pro-rated warranty of 3 years with an expectant life of 4 years. 
Easy to change, a sensor is included when you buy an O2EII analyser.

Advisory Note:

Replacement oxygen cells for the O2EII should only be purchased when required. 
Analox do not recommend that spare cells are bought when purchasing your O2EII. 
Electrochemical sensors are consumable items. 
We therefore cannot credit sensors if incorrect orders have been placed. 
This does not affect your warranty..