Page "Telephone card" Paragraph 5

The next technology used optical storage.

Optical phone cards get their name from optical structure embossed inside the cards.

This optical structure is heated and destroyed after use of the units.

Visible marks are left on the top of the cards, so that the user can see the balance of remaining units.

Optical cards were produced by Landis + Gyr and Sodeco from Switzerland and were popular early phonecards in many countries with first optical phonecards successfully introduced in 1977 in Belgium.

Such technology was very secure and not easily hackable but chip cards phased out the optical phone cards around the world and the last Landis + Gyr factory closed in May 2006 when optical phonecards were still in use in few countries like Austria, Israël and Egypt.