Citizen once made a series of watches powered only by the temperature difference between the wearers skin and the ambient air
Citizen Eco-Drive Thermo watches were introduced in 1999 and use the temperature difference between the wearer’s arm and the surrounding environment as a power source. The rare Eco-Drive Thermo watches use the Seebeck effect to generate thermo electricity that powers the electronic movement and charges the secondary power cell. In the sun or in the tropics the ambient temperature can come close to or exceed the temperature of the wearer’s wrist causing the watch to stop generating thermo electricity. In case no power is generated, an Eco-Drive Thermo movement will save power by moving the second hand in ten second increments until the production of thermo electricity is resumed. Citizen has stopped making Eco-Drive Thermo watches.
Hybrid Eco-Drive movements
Citizen also built an automatic quartz powered watch, the Citizen Promaster Eco-Duo Drive (released in December 1998). Novel to this watch was the use of both mechanical power as well as a solar cell to power the electronic movement and charge the secondary power cell. This model was an attempt to enter higher-priced markets (at a cost of around $1,000 USD). The Eco-Duo Drive technology failed to attract consumer interest and Citizen has since stopped making use of the unique movement.
Solar cell and secondary battery life expectancy
According to Citizen, experimental data showed the solar cell and secondary battery will last for more than 10 years. According to Citizen Europe, laboratory tests showed that after 20 years the secondary battery retains a power storage capacity of 80% of its initial capacity.
For water resistant and diving Eco-Drive watches Citizen recommends a watch gasket exchange every 2 or 3 years to preserve their water resistance because watch gaskets which form a watertight seal degrade as they age. Further Citizen recommends maintenance for Eco-Drive watch movements in regular intervals in order to extend the life of the watch movement, since the gears used in running watch movements are subject to slow wear. Citizen states that their lubricants for Long-Lasting Precision Equipment when used in watches, timepiece movements remain smooth for a long time as the oil does not harden even after 20 years