The legless key is functionally identical to the leg key. The key's terminals are located at the rear of the base on the top side of the key. This example appears to be a military version manufactured by Bunnell. The sounder transforms the current pulses in the telegraph wire into audible clicking sounds which are interpreted by the telegrapher. Two vertical solenoids form a horseshoe magnet.
Current pulses energize the magnet which then attracts the armature.
The armature is attached to a spring loaded lever. The lever strikes the lower portion of the anvil, producing an audible click. Another audible click is produced when the lever strikes the upper portion of the anvil upon cessation of the current. The lever has knurled screws and jam nuts that allow the spacing of the armature from the magnet and the lever travel to be adjusted. Another screw adjusts the spring tension.