Related Rule
Switzerland
Practice Relating to Rule 37. Open Towns and Non-Defended Localities
Section B. Establishment of non-defended localities
Switzerland’s Basic Military Manual (1987) states:
Through reciprocal specific declarations, the Parties to the conflict can designate non-defended localities or demilitarized zones (the latter already in peacetime). These localities or zones have to fulfil the following conditions:
a. all combatants, as well as mobile weapons and military equipment, must be evacuated;
b. no hostile use shall be made of fixed military installations or establishments;
c. no acts of hostility shall be committed by the authorities or by the population;
d. any activity in support to the military effort must cease;
e. the localities/zones must be marked by a distinctive sign.
Police forces may be maintained in these localities and zone for the purpose of maintaining law and order.
Non-defended localities/zones must not be abused for military purposes, for they will lose their protected status. 
Switzerland, Lois et coutumes de la guerre (Extrait et commentaire), Règlement 51.7/II f, Armée Suisse, 1987, Article 32; see also Article 12(2).