The border between Liechtenstein and Switzerland has been open since 1923. However, now Liechtenstein is outside the Schengen area and must have a border with Switzerland. At the same time, as Travel.ru notes, this border does not actually exist.
Liechtenstein initiated its entry into Schengen as early as June 21, 2006. All agreements have been signed and ratified, but not all procedures for the country's accession to the Schengen area have been completed, and at present Liechtenstein is not a member state of the Schengen Agreement.
Currently, Switzerland is tasked with monitoring the entry of all persons into the Schengen territory if they cross the Swiss border. The authorities of the two countries have found a compromise solution. The Liechtenstein-Switzerland border will be monitored using forty video cameras. In addition, the long-existing border crossing between Liechtenstein and Austria at Schaanwald-Tisis will be switched to 24-hour operation, and its staff will respond urgently if any violations are spotted on the adjacent Swiss-Liechtenstein border.
Special measures have been taken regarding third-country nationals legally residing in Liechtenstein. Previously, they could freely enter Switzerland. For those people who have a residence permit from Liechtenstein and need a Schengen visa, it will be issued free of charge.