The movements are characterised by: Tuning Fork (from Omega's Cal. 1220 on the right ) A Transistor acting as a switch No Mechanical contacts

There is a lot of literature on the Internet describing the history and development of Bulova Accutron, the first tuning fork watch, so I'm not going to repeat it on this site. But as a very brief introduction, the tuning fork watch is like no other battery driven watch, or mechanical for that matter: it is driven by a tuning fork vibrating at 300-720 times a second, depending on the model; as a result, it doesn't tick, but hummms. The index mechanism also means the tuning fork watches are characterised by a constant sweeping seconds hand.

Some good links are:

• Accutron: Max Hetzel, the Man behind the Invention
• The Accutron Watch Page
• The Amazing Bulova Accutron

Nearly all of the hummers have a microscopic indexing system that converts the tuning fork's vibrations into a rotary action to drive the hands. This Index Wheel is at the heart of the movement; it is easily damaged; it has 300+ teeth:

The first set of photograps show the Accutron 214 and 2180 movements. These two movements (or variants of) feature in all the Bulova Accutron watches features here.

Often referred to as the Rolls-Royce of hummers, the ESA 9162 featured in many watches including the Omega F300 and the Tissot Tissonic:

But without doubt, the most unique and strangest tuning fork watch ever made was the Omega Cal. 1220 / 1230 or Megasonic movement (photo below). This awesome, and rare, movement featured: an asymmetric tuning fork resonating at 720 Hz instead of the more usual 300 Hz, a very unusual micromotor attached to one of the tuning fork tines and a series of magetic gears! Read much more about this wonderful movement in the Omega section.