Membrane keyboard

Smaller, specialized membrane keyboards, typically numeric-and-a-few-control-keys only, have been used in access control systems (for buildings and restricted areas), simple handheld calculators, domestic remote control keypads, microwave ovens, and other similar devices where the amount of typing is relatively small or infrequent, such as cell phones.

[5][1] Under normal conditions, the switch (key) is open, because current cannot cross the non-conductive gap between the traces on the bottom layer.

The conductive traces on the underside of the top layer can then bridge the gap, allowing current to flow.

For additional wear resistance, a simple, easily replaceable protective clear sheet can be placed in front of the membrane.

Membrane keyboards are widely used in consumer electronics, industrial, commercial, scientific and military equipment.

Membrane keyboard as used on the East German Robotron Z1013 .
Cross-section diagram of a typical membrane keyboard. The thickness of the bottom three layers has been exaggerated for clarity; in reality, they are not much thicker than pieces of paper or thin cardstock.
Internal layers of a modern full-travel computer keyboard; bottom contact layer, spacer layer with holes, top contact layer, then elastomer top layer to provide restoring force to keytops.