I keep one until the battery dies. Then I replace the battery with a second rechargeable lithium and a new watch band. By the next time the next battery goes dead, the case is shot, too. Make absolutely sure that you follow the battery replacement directions carefully, reading the directions fully BEFORE attempting it. There are very tiny parts that can drop out and easily lost.
I spent a few nights in a straw bale home, wanting to experience what they were like. They are incredibly quiet. Each bale is 1.5 ft of soundproofing/insulation. The loudest part of the house was the clock ticking. The house was heated by appliances such as the refrigerator and water heater. A local monastery built several to rent out for people wanting a tranquil contemplation.