Analog altimeters typically use a sealed chamber, which expands or contracts depending on the air pressure. This drives a spring, which then turns the needle of the altimeter. Well-designed metal springs can have lifetimes of several thousand cycles, and analog altimeter failures are quite rare (but they have been known to happen).
In contrast, Tritium uses a microelectromechanical system (or MEMS for short) to sense the air pressure. The MEMS sensor is a microscopically etched piece of extremely pure silicon crystal which senses the air pressure and transmits this value to a microcontroller.
Due to the mechanical properties of silicon, MEMS sensors typically have service lifetimes of up to billions or trillions of cycles. The MEMS sensor in Tritium is manufactured by the German company Bosch, and represents the latest in technology with a resolution of less than 17cm (6.6 inches)!**